Buttery Roast Beef Sliders with Caramelized Onions

hand holds a roast beef slider dripping with au jus above a bowl

4.91 from 10 votes

Buttery Roast Beef Sliders with Caramelized Onions

If there’s one thing I’ll never turn down, it’s a buttery, cheesy slider—especially when it’s piled high with tender roast beef, sweet caramelized onions, and a swipe of creamy garlic aioli. Slathered in garlic butter and dunked into homemade au jus, these are everything you want in a party dish!

Prep Time15

Cook Time55

Total Time1 10

Course: Appetizers

Cuisine: American

Servings: sliders

Calories: 375kcal

Author: Eden Westbrook

Ingredients

For the Caramelized Onions

2 tablespoons unsalted butter
1 tablespoon olive oil
3 large yellow onions thinly sliced
½ teaspoon kosher salt
1 teaspoon brown sugar optional, helps speed up caramelization
2 tablespoons beef broth for deglazing

For the Homemade Garlic Aioli

1 large egg yolk room temperature
1 teaspoon Dijon mustard
1 garlic clove finely grated or minced
1 tablespoon fresh lemon juice
½ cup light olive oil or neutral oil
Kosher salt to taste

For the Au Jus Sauce

¼ cup unsalted butter
1 tablespoon Better than Bouillon Beef Base
2 cups beef broth
2 teaspoons Worcestershire sauce

For the Roast Beef Sliders

12 slider buns sliced in half (Hawaiian rolls, preferred)
¼ cup homemade garlic aioli or mayonnaise
½ pound deli roast beef thinly sliced
12 slices melty cheese like provolone, Swiss, or muenster
½ cup shredded mozzarella cheese
2 cups caramelized onions

For the Garlic Butter Sauce

6 tablespoons unsalted butter melted
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

Instructions

Make the Caramelized Onions

Melt the butter and olive oil in a large skillet over medium-low heat.
2 tablespoons unsalted butter, 1 tablespoon olive oil
Add the sliced onions, sprinkle in the salt and brown sugar, and cook low and slow, stirring occasionally, until the onions are soft, deep golden brown, and jammy — about 35–45 minutes. Stir in the beef broth at the end to deglaze the pan and pick up all that good flavor. Set aside.
3 large yellow onions, ½ teaspoon kosher salt, 1 teaspoon brown sugar, 2 tablespoons beef broth

Make the Garlic Aioli

In a small bowl, whisk together the egg yolk, Dijon mustard, grated garlic, and lemon juice until smooth.
1 large egg yolk, 1 teaspoon Dijon mustard, 1 garlic clove, 1 tablespoon fresh lemon juice
While blending with an immersion blender or using a whisk, slowly stream in the oil until the mixture thickens into a creamy aioli. Season with a pinch of salt and set it aside. (If you’re using mayo instead for an easier version, just stir in the garlic, mustard, lemon, and salt!)
½ cup light olive oil or neutral oil, Kosher salt

Get the Au Jus Started

Melt the butter in a medium saucepan over medium heat. Stir in the Better than Bouillon beef base, beef broth, and Worcestershire sauce. Let it simmer for 15–20 minutes until it reduces by about half. It’ll darken slightly and thicken a little as it cools. Keep warm for serving.
¼ cup unsalted butter, 1 tablespoon Better than Bouillon Beef Base, 2 cups beef broth, 2 teaspoons Worcestershire sauce

Toast the Bottom Buns

Preheat your oven to 350°F (180℃ or Gas Mark 5)
Slice the buns in half horizontally without separating them. Place the bottom buns, cut-side up, on a parchment-lined baking sheet. Brush lightly with melted butte or aioli and toast for 5 minutes until just golden.
12 slider buns

Assemble the Sliders

Spread a generous layer of garlic aioli over the toasted bottom buns. Pile the roast beef evenly over the buns — 2–3 layers deep for hearty sliders.
¼ cup homemade garlic aioli or mayonnaise, ½ pound deli roast beef
Lay down your slices of cheese, then sprinkle the shredded mozzarella over the top for extra meltiness.
12 slices melty cheese, ½ cup shredded mozzarella cheese
Spoon an even layer of caramelized onions across the sliders.
2 cups caramelized onions
Place the top half of the rolls on the sliders. In a small bowl, mix together the melted butter, Worcestershire, poppy seeds, sesame seeds, garlic powder, dried minced onion, salt, and pepper. Generously brush the tops of the rolls with the garlic butter mixture.
6 tablespoons 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
Cover loosely with foil and bake for 10 minutes. Remove the foil and bake for another 5–10 minutes, until the tops are golden brown and the cheese is nice and melty.
Slice between the rolls to separate the sliders. Serve warm with little bowls of au jus on the side for dipping!

Notes

30 Minute Instructions

Jazz up mayo with the aioli ingredients, and bake the sliders without the caramelized onions for easy roast beef sliders in half the time!

Make Ahead and Storage Instructions

Make Ahead: Build the sliders up to two days ahead of time on a rimmed baking sheet or baking dish without the caramelized onions or garlic butter.

Before serving, make the garlic butter and top the sliders with the onions and bake as directed.

Storing: Keep your leftover French Dip sliders in an airtight container for up to 3 days.

Reheating Instructions: Reheat the leftovers in the oven at 375ºF for about 10 minutes so they don't get soggy!

Nutrition