These French Dip Sliders are loaded with savory roast beef, melted provolone, and caramelized onions on soft slider buns. Served with warm beef broth for dipping, they make an easy and crowd-pleasing meal or party appetizer.
Preheat the oven to 350°F (175°C). Lightly grease a baking dish or line it with foil.
In a skillet over medium heat, warm the olive oil and 2 tablespoons butter. Add the sliced onion and cook for 6 to 8 minutes, stirring occasionally, until soft and lightly caramelized.
Stir in the garlic powder and Worcestershire sauce, then add the roast beef. Toss just until warmed through, about 1 to 2 minutes. Remove from heat.
In a small saucepan, heat the beef broth with dried thyme, salt, and black pepper until hot. Keep warm for serving as the dipping sauce.
Slice the slider buns in half horizontally and place the bottom halves in the prepared baking dish. Layer on the warm roast beef mixture and top with provolone cheese. Add the top halves of the buns.
In a small bowl, mix the melted butter with Dijon mustard and poppy seeds. Brush the mixture over the tops of the sliders.
Cover the dish with foil and bake for 10 minutes. Remove the foil and bake for 5 to 7 minutes more, until the tops are golden and the cheese is melted.
Serve the sliders warm with the hot beef broth on the side for dipping.
Notes
You can use leftover roast beef for an easy shortcut. For extra flavor, add a little more thyme or a slice of cheese to each slider. Serve immediately so the buns stay soft and the cheese remains melty.