If you’re craving something irresistibly savory and utterly comforting, this Buttery Roast Beef Sliders with Caramelized Onions Recipe is about to become your new go-to. Imagine tender roast beef, melty cheese, and sweet onions all tucked in soft buttery buns—pure slider perfection!

The image shows a close-up of two stacked sandwiches on a wooden board. Each sandwich has three main layers: the top and bottom are golden brown toasted buns sprinkled with sesame seeds and seasoning, the middle layer is melted light yellow cheese with caramelized onions that are juicy and golden, and there is a layer of thin slices of cooked meat underneath the cheese. Some melted cheese and onions are dripping out from the sides, making the sandwich look rich and full. The background is dark, and the wood texture underneath contrasts with the food. photo taken with an iphone --ar 2:3 --v 7

Jump to:

Why You'll Love This Recipe
Ingredients & Why They Work
Make It Your Way
Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe
Top Tip
How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe
Make Ahead and Storage
Frequently Asked Questions:
Final Thoughts
Buttery Roast Beef Sliders with Caramelized Onions Recipe

Why You'll Love This Recipe

I’ve made these sliders countless times for game days and family gatherings, and every single time they’re the first to disappear. The combination of buttery buns, caramelized onions, and homemade garlic aioli is a total crowd-pleaser.

Loaded with Flavor: Every bite delivers rich roast beef paired with sweet caramelized onions and savory garlic aioli.
Perfect for Entertaining: These sliders make an easy, impressive centerpiece at any party or family meal.
Homemade Touches: From scratch aioli and au jus sauce elevate these sliders beyond your typical sandwich.
Simple but Showstopping: Despite layered flavors, the recipe is straightforward and totally doable in about an hour.

Ingredients & Why They Work

Gathering the right ingredients is half the fun—and the secret to making these sliders truly shine. A few tips before you start: grab good quality deli roast beef—think thinly sliced and tender. For the buns, Hawaiian rolls work beautifully because their natural sweetness balances the savory beef and onions perfectly.

Flat lay of a cluster of 3 large yellow onions, thinly sliced in a small white ceramic bowl, a small white bowl of unsalted butter cubes, a small white bowl with olive oil, a small white bowl of light olive oil, a clean large whole brown egg with uncracked shell, a small white bowl with Dijon mustard, a single fresh garlic clove, a small white bowl of fresh lemon juice, a small white bowl with kosher salt, a small white bowl with brown sugar, a small white bowl with finely shredded mozzarella cheese, a stack of thinly sliced deli roast beef, a neat pile of sliced provolone cheese, a cluster of 12 Hawaiian slider buns halved horizontally, a small white bowl with Worcestershire sauce, a small white bowl with poppy seeds, a small white bowl with white sesame seeds, a small white bowl with garlic powder, a small white bowl with dried minced onion, a small white bowl of freshly cracked black pepper, all arranged symmetrically on a clean white marble surface, soft natural light, photo taken with an iPhone, professional food photography style, fresh ingredients, white ceramic bowls, no bottles, no duplicates, no utensils, no packaging --ar 2:3 --v 7 --p m7354615311229779997

Unsalted Butter: Essential for caramelizing onions and making the garlic butter sauce rich and luscious.
Olive Oil: Helps the onions cook evenly without burning, keeping them soft and sweet.
Yellow Onions: Their natural sugars develop beautifully during caramelization, adding depth to the sliders.
Kosher Salt: Highlights the flavors without overpowering; I always use this for the best seasoning control.
Brown Sugar: Speeds up caramelization to get those jammy onions with a hint of sweetness.
Beef Broth: Adds umami dimension and helps deglaze the pan for the onions and au jus sauce.
Egg Yolk: Key to making a creamy, homemade garlic aioli that beats store-bought every time.
Dijon Mustard: Adds a nice tang that brightens up the aioli just right.
Garlic: Fresh, finely grated garlic punches up the flavor in the sauce and aioli.
Lemon Juice: Brings balance and freshness to the aioli to keep it from feeling too heavy.
Light Olive or Neutral Oil: Used to emulsify the aioli smoothly without overpowering flavors.
Better than Bouillon Beef Base: Concentrated, flavorful, and easy to work with for a rich au jus.
Worcestershire Sauce: Adds deep savoriness to both the au jus and the garlic butter sauce.
Slider Buns (Hawaiian Rolls preferred): Sweet, soft, and buttery, these buns hold everything beautifully without falling apart.
Deli Roast Beef: Thinly sliced for perfect layering and tender bites in every slider.
Melty Cheese (Provolone, Swiss or Muenster): Melts beautifully over the meat creating that gooey, cheese pull everyone loves.
Shredded Mozzarella Cheese: Sprinkled on top for extra gooey meltiness and flavor.
Poppy Seeds and White Sesame Seeds: Bring subtle nuttiness and crunch to the garlic butter brushed on top.
Garlic Powder and Dried Minced Onion: Boost the savory notes in the garlic butter sauce.
Black Pepper: Freshly cracked for a zing that wakes up all the rich flavors.

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Note: You'll find the complete list of ingredients, along with their exact measurements, in the printable recipe card at the bottom of this post.

Make It Your Way

The beauty of this Buttery Roast Beef Sliders with Caramelized Onions Recipe is how easily you can customize it to fit your tastes or the occasion. Whether you want to streamline the prep or add a little twist, these sliders can do it all!

Quick Version: If you’re short on time, swap out the homemade garlic aioli for a good-quality garlic mayo and skip the caramelized onions. Bake the sliders directly for about 30 minutes—you’ll still get that melty, buttery goodness with much less fuss.
Make-Ahead Magic: Feeling ambitious? Assemble your sliders up to two days in advance without the onions and garlic butter. Keep them chilled on a rimmed baking sheet, then add those flavorful finishing touches right before baking. It’s perfect for entertaining without the last-minute rush.
Cheese Choices: I love using provolone for its mild meltiness, but Swiss or muenster work beautifully too. Or try a combo for a custom cheese pull that will impress everyone!
Spice It Up: For a little extra kick, mix some horseradish into the aioli or sprinkle a dash of smoked paprika over the caramelized onions before layering. Just enough heat to keep things interesting.
Low Lactose Tip: Since this recipe uses cheeses like provolone and Swiss, it’s naturally lower in lactose, making it easier on sensitive stomachs without sacrificing flavor.

Step-by-Step: How I Make Buttery Roast Beef Sliders with Caramelized Onions Recipe

A woman's hand is holding a sandwich made with a toasted, golden-brown sesame seed bun, dripping with thick brown gravy. Inside the sandwich, there are multiple layers of soft, thin slices of cooked meat and melted cheese with a creamy texture, visible just under the bun. Below the sandwich, a white bowl filled with rich brown gravy has some gravy dripping down its side onto a dark wooden surface. Behind the bowl, several more sandwiches with the same sesame seed buns, meat, and cheese are stacked, showing their melted cheese and crispy textures. The whole scene is set on a white marbled surface with a blurred dark shirt in the background, capturing the warm, messy, and inviting aspect of the dish. photo taken with an iphone --ar 2:3 --v 7

Step 1: Slowly Caramelize Those Onions

Start by melting 2 tablespoons of unsalted butter with 1 tablespoon of olive oil in a large skillet over medium-low heat. The key here is patience—add your thinly sliced 3 large yellow onions along with ½ teaspoon kosher salt and 1 teaspoon brown sugar (this really helps speed up caramelization). Cook them low and slow, stirring occasionally, for about 45 minutes until they’re soft, jammy, and a beautiful golden brown. Towards the end, stir in 2 tablespoons of beef broth to deglaze the pan and catch all those flavorful browned bits. You’ll smell the sweetness and rich depth develop as they cook—this step really elevates the whole slider!

Step 2: Whip Up That Creamy Garlic Aioli

In a small bowl, whisk together 1 large room-temperature egg yolk, 1 teaspoon Dijon mustard, 1 finely grated garlic clove, and 1 tablespoon fresh lemon juice until smooth. Then, slowly drizzle in ½ cup of light olive or neutral oil while whisking vigorously or using an immersion blender. This gradual process thickens the mixture into a luscious aioli perfect for spreading. Don’t forget to season with kosher salt to taste! If the idea of making aioli from scratch feels intimidating, no worries — just mix these flavors into mayonnaise instead for a quick shortcut that’s still packed with flavor.

Step 3: Simmer the Savory Au Jus Sauce

Melt ¼ cup unsalted butter in a medium saucepan over medium heat, then stir in 1 tablespoon Better than Bouillon Beef Base, 2 cups beef broth, and 2 teaspoons Worcestershire sauce. Let this gently simmer for about 20 minutes until it reduces by half and thickens slightly. This rich au jus will be your dipping companion, adding juicy goodness to every slider bite.

Step 4: Toast the Slider Buns

Preheat your oven to 350°F (180°C). Slice your 12 slider buns in half horizontally—don’t separate the halves—and place the bottom buns cut-side up on a parchment-lined baking sheet. Lightly brush each with melted butter or a touch of your homemade aioli, then toast for about 5 minutes until just golden. This adds a buttery crispness and holds everything together perfectly.

Step 5: Assemble Those Sliders Like a Pro

Begin by spreading a generous layer of the garlic aioli over each toasted bottom bun. Then pile on the roast beef—aim for 2 to 3 thin layers per slider for that hearty, satisfying bite. Next, top with 12 slices of your chosen melty cheese, followed by a sprinkle of ½ cup shredded mozzarella for extra gooey melt. Finally, spoon on 2 cups of those golden caramelized onions, spreading evenly to keep every bite balanced with sweetness and richness.

Step 6: Brush on Garlic Butter and Bake to Melty Perfection

Place the tops of the buns on your sliders. In a small bowl, mix together 6 tablespoons melted unsalted butter, 1 teaspoon Worcestershire sauce, 1 tablespoon poppy seeds, 1 tablespoon white sesame seeds, ½ tablespoon garlic powder, ½ tablespoon dried minced onion, ½ teaspoon kosher salt, and freshly cracked black pepper to taste. Brush this flavorful garlic butter mixture generously over the slider tops. Cover the tray loosely with foil, bake for 10 minutes, then remove the foil and bake another 10 minutes until the tops turn a gorgeous golden brown and the cheese is melted and bubbly. The aroma alone will have everyone eager to dig in!

Step 7: Serve Warm with Au Jus for Dipping

Carefully slice between each roll to separate your sliders. Serve them warm with small bowls of the rich au jus sauce on the side for dipping. That savory, buttery, cheesy combo is truly irresistible—perfect for game day, parties, or anytime comfort food cravings strike.

Top Tip

Mastering these Buttery Roast Beef Sliders with Caramelized Onions Recipe is all about layering flavors and textures thoughtfully. These tips will make sure your sliders come out perfectly every time!

Low and Slow Caramelization: Cooking the onions gently over medium-low heat for about 45 minutes creates that sweet, jammy texture that really makes the sliders stand out.
Freshly Made Garlic Aioli: Homemade aioli with fresh garlic and lemon juice adds brightness and richness you just can’t get from store-bought mayo.
Butter Brush Magic: Don’t skimp on brushing the slider tops with the garlic butter mixture before baking — it crisps up the buns and adds a beautiful golden sheen.
Don’t Rush the Bake: Covering the sliders with foil during the first baking stage keeps them moist and melty; removing the foil later gives that perfect caramelized finish.

How to Serve Buttery Roast Beef Sliders with Caramelized Onions Recipe

A tan baking tray holds five slices of light yellow bread with a soft texture. Each slice is spread with a layer of creamy white mayonnaise, which is smooth with small bits of green herbs mixed in. The slices are arranged close together, with three on the bottom and two on the top, placed on a white marbled surface. Photo taken with an iphone --ar 2:3 --v 7

Garnishes

Sprinkle fresh chopped parsley or chives on top of the sliders just before serving to add a pop of color and a touch of herbal freshness. A light drizzle of extra garlic aioli or a smear of spicy mustard can also elevate the flavor even more.

Side Dishes

These sliders pair beautifully with crispy kettle-cooked potato chips, a simple mixed green salad with a tangy vinaigrette, or classic coleslaw to balance the richness. For a heartier meal, serve alongside sweet potato fries or a bowl of creamy mac and cheese.

Make Ahead and Storage

Storing Leftovers

Store any leftover Buttery Roast Beef Sliders with Caramelized Onions in an airtight container in the refrigerator for up to 3 days. Keeping them well sealed helps maintain their fresh, melty texture without drying out.

Freezing

If you'd like to freeze the sliders, assemble them without the caramelized onions and garlic butter tops, then wrap tightly in plastic wrap and foil. Freeze for up to 1 month. Thaw overnight in the fridge before adding toppings and baking as instructed.

Reheating

To reheat leftovers without sogginess, place sliders on a baking sheet and warm in a preheated 375°F oven for about 10 minutes. This will melt the cheese nicely and keep the buns toasted and flavorful.

Frequently Asked Questions:

Can I make the caramelized onions ahead of time?

Absolutely! Caramelized onions can be prepared up to 3 days in advance and stored in the refrigerator. Just reheat gently when you’re ready to assemble your sliders.

What cheese works best for these sliders?

Provolone, Swiss, and muenster are all excellent choices because they melt beautifully and complement the roast beef’s flavor. The shredded mozzarella adds extra gooeyness.

Is it safe to make the aioli with raw egg yolk?

If you’re concerned about raw egg, use pasteurized eggs or substitute with a garlic mayonnaise blend. The mayo option still delivers that creamy garlicky kick and is easier for busy days.

Can I substitute slider buns?

Hawaiian rolls are preferred for their sweetness and softness, but you can use any small slider buns you like. Just make sure they’re sturdy enough to hold all the juicy fillings!

Final Thoughts

These Buttery Roast Beef Sliders with Caramelized Onions have quickly become a favorite for game days, parties, or cozy dinners at home. There’s something so comforting about layers of tender beef, melty cheese, and sweet onions hugging buttery buns. I hope you enjoy making and sharing this recipe as much as I do — happy cooking and even happier eating!