1. Preheat the oven to 325°F and prepare a 9×13-inch baking dish with nonstick cooking spray.
2. Slice the rolls horizontally while keeping them attached, and place the bottom half in the dish.
3. Spread raspberry preserves on the bottom half if desired.
4. Layer with half of the Swiss cheese slices, followed by the ham, turkey, and the remaining cheese.
5. Place the top half of the rolls over the filling.
6. In a small bowl, whisk together the melted butter, egg, pepper, Worcestershire sauce, Dijon mustard, and mayonnaise. Spread this mixture on the inside of the top half of the rolls.
7. Brush the remaining butter mixture over the tops and sides of the sliders.
8. Bake uncovered for 25-30 minutes, or until the cheese is melted and the buns are toasted. Loosely cover with foil if the tops brown too quickly.
9. Remove from the oven, sprinkle with powdered sugar, and serve with jam on the side if desired.