After removing the sweet rolls from the packaging, place them on a cutting board and slice horizontally to divide the rolls into top and bottom halves.
Lay the bottom portion in a greased 9x9-inch baking dish, then evenly spread horseradish sauce over the cut sides.
Place two folded slices of ham on each roll, add shredded white cheddar cheese, and season with ground pepper.
Next, arrange dill pickles on top of the ham and cheese, then layer with Swiss cheese slices.
Sprinkle garlic powder for extra flavor. Place the top halves of the rolls back on and press gently to secure the sandwiches.
In a skillet, melt butter over medium heat.
Once melted, transfer to a bowl and whisk in onions, spicy brown mustard, brown sugar, and Worcestershire sauce.
Drizzle this mixture evenly over the sandwiches, cover with foil, and refrigerate for several hours or overnight.
When ready to bake, preheat the oven to 350°F.
Bake the sliders covered for 25 minutes, then uncover and bake for an additional 5-10 minutes until golden.
Garnish with fresh parsley and serve immediately.