Preheat the oven to 350 degrees F. Heat a nonstick skillet over medium heat. Add the sliced onion and cook for 6–8 minutes, stirring occasionally, until softened and lightly golden.

Slice the slider rolls horizontally without separating the individual rolls. Place the bottom half in a baking dish. Layer on the roast beef, cooked onions, and cheese. Place the top half of the rolls over the cheese.

Mix the melted light butter, Worcestershire sauce, garlic powder, parsley, and onion powder. Brush evenly over the tops of the rolls.

Cover loosely with foil and bake for 10 minutes. Remove the foil and bake for another 5–8 minutes, until the cheese has melted and the tops are lightly golden.

While the sliders bake, combine the beef broth, Worcestershire sauce, garlic powder, and onion powder in a saucepan.

Bring to a gentle simmer and cook for 5 minutes. If you prefer a slightly thicker dip, stir in the cornstarch slurry and simmer until slightly thickened.

Let the sliders rest for 2–3 minutes, cut apart, and serve warm with individual cups of au jus for dipping.