Preheat the oven to 375°F (190°C).

Slice the slider buns in half horizontally and place the bottom halves in a greased baking dish.

In a small bowl, mix together the mayonnaise, Dijon mustard, garlic powder, onion powder, and black pepper. Spread this mixture evenly over the bottom halves of the buns.

Layer the thinly sliced roast beef evenly on top of the buns, followed by the provolone cheese slices.

Place the top halves of the buns over the cheese to complete the sliders.

Brush the melted butter over the tops of the buns.

Cover the baking dish with aluminum foil and bake for 15 minutes, then remove the foil and bake for an additional 5 minutes until the buns are golden and the cheese is melted.

While the sliders are baking, prepare the au jus gravy. Heat olive oil in a skillet over medium heat, then sauté the sliced onions until softened and caramelized, about 5-7 minutes.

Add the beef broth, Worcestershire sauce, and soy sauce to the skillet with the onions. Bring the mixture to a gentle simmer and cook for 5 minutes, stirring occasionally.

Strain the au jus into a serving bowl, leaving the onions out if desired, or serve them alongside the sliders.

Remove the sliders from the oven and let them cool for 2 minutes. Serve warm with the au jus gravy for dipping.