Step 1: Prep the Baking Dish
Preheat your oven to 350°F. Lightly grease a 9×13-inch baking dish with butter or cooking spray. This prevents sticking and makes cleanup easier.

Step 2: Slice the Rolls
Without separating the individual rolls, use a sharp serrated knife to slice the entire block of rolls horizontally, creating a top and bottom layer. Keep them connected – this is key to easy assembly! Place the bottom half in your prepared baking dish.

Step 3: Add Mustard (Optional)
If using, spread a thin layer of Dijon mustard evenly over the bottom half of the rolls. This adds a tangy flavor that cuts through the richness of the beef and cheese.

Step 4: Layer the Roast Beef
Evenly distribute the roast beef over the bottom rolls, covering them completely. Fold or layer the meat so each slider gets a good amount. If using caramelized onions, add them now on top of the beef.

Step 5: Add the Cheese
Layer the Swiss or provolone cheese slices over the roast beef, making sure to cover all the meat. Overlap slices as needed to ensure every slider gets melty cheese. If using shredded cheese, sprinkle it evenly over the beef.

Step 6: Top with Upper Buns
Carefully place the top half of the rolls over the cheese layer, maintaining the connected structure. Press down gently to compact the layers slightly.

Step 7: Make the Garlic Butter
In a small saucepan over low heat, melt the butter. Add the minced garlic, Worcestershire sauce, dried parsley, onion powder, salt, and pepper. Stir well and let it cook for 1-2 minutes until fragrant but not browned. Remove from heat.

Step 8: Brush with Garlic Butter
Using a pastry brush or spoon, generously brush the garlic butter mixture over the tops of the rolls, making sure to get in all the crevices between rolls. Use all of the butter mixture – don’t be shy! This creates that gorgeous golden crust.

Step 9: Cover and Bake
Cover the baking dish tightly with aluminum foil. Bake for 15 minutes. This allows the cheese to melt and the sliders to heat through without over-browning the tops.

Step 10: Uncover and Finish
Remove the foil and bake for an additional 5-7 minutes, or until the tops are golden brown and slightly crispy. Watch carefully during this stage to prevent burning.

Step 11: Prepare the Au Jus
While the sliders bake, combine beef broth, Worcestershire sauce, soy sauce, garlic powder, and onion powder in a small saucepan. Heat over medium heat until simmering. Taste and adjust seasoning with salt and pepper. Keep warm on low heat. If your sliders released any drippings, add them to the au jus for extra flavor.

Step 12: Serve
Remove the sliders from the oven and let them rest for 2-3 minutes. Cut along the scored lines to separate individual sliders. Serve immediately with warm au jus in small bowls for dipping.