01 -
Set your oven to 350°F and let it warm up.
02 -
Melt 3 tablespoons of butter in a big frying pan on medium heat. Stir in the onions and cook on low for 10-12 minutes, stirring occasionally, until they start to brown. Mix in the minced garlic and rosemary, then cook for another 5 minutes until they’re fully soft and golden. Remove from the stove and let cool.
03 -
Lay parchment paper over a sheet pan. Arrange the buns on the tray, slice them in half, and set the bun tops aside.
04 -
Start by layering roast beef over the bottom buns. Add slices of cheese to cover the meat. Spread the caramelized onions over the cheese, and finish by putting the bun tops back on.
05 -
Mix together the melted butter, mustard powder, parsley, and garlic powder in a small bowl until combined.
06 -
Brush the melted butter mixture all over the tops and edges of the buns.
07 -
Put the tray of assembled sliders into the oven. Bake for about 5-8 minutes, or until the cheese has melted well and the buns are golden brown.
08 -
After removing the sliders from the oven, let them sit for a few minutes to cool slightly. Cut them apart or pull them apart by hand, then dig in and enjoy!