Preparation

• Gather all ingredients. Preheat the oven to 350 degrees F (180 degrees C). Grease a 9x13-inch baking dish.
• Slice the slider buns in half horizontally without separating them, and place the bottom half in the prepared dish.
• In a heavy skillet over medium heat, melt 1 tablespoon butter; add onion and cook, stirring occasionally, until soft and golden, 8 to 10 minutes.
• Layer roast beef evenly over bottom buns, then layer cheese slices over beef. Scatter caramelized onion over cheese, and add top buns back on.
• Melt remaining butter and stir in garlic powder, Worcestershire sauce, and parsley; brush over tops of buns. Cover with foil.
• Bake in the preheated oven for 15 minutes. Uncover and bake until tops are golden and cheese is melted, about 5 minutes more.
• Meanwhile, for jus, combine bone broth, Worcestershire, soy sauce, garlic powder, onion powder, and fish sauce in a small saucepan. Bring to a simmer, stirring occasionally, over medium heat.
• Stir cornstarch and water together in a small bowl to create a smooth slurry; add to the broth, and simmer until slightly thickened, 2 to 3 minutes.
• Serve sliders with the jus for dipping.