Step 1

Arrange a rack in the middle of the oven and heat the oven to 350°F.

Step 2

Place 4 tablespoons unsalted butter in a small, microwave-safe bowl and microwave until melted, 20 to 30 seconds. (Alternatively, melt butter in a small saucepan over medium heat.) Add 1 tablespoon Dijon mustard, 1 teaspoon Worcestershire sauce, 1/2 teaspoon onion powder, and 1/4 teaspoon kosher salt, and whisk to combine.

Step 3

Without separating the rolls, cut 1 package Hawaiian sweet dinner rolls in half horizontally with a serrated knife. Place the bottom half of the rolls in a 9x13-inch or 7x11-inch baking dish.

Step 4

Arrange 6 slices of the Swiss cheese on the rolls, overlapping the slices as needed to completely cover. Fold and arrange 12 thin slices ham over the cheese, arranging a slice on each roll. Layer the remaining 6 slices Swiss cheese over the ham. Place the top half of the rolls over the cheese.

Step 5

Brush the butter onto the top of the rolls, then sprinkle with 1 teaspoon poppy seeds. Cover the baking dish tightly with aluminum foil.

Step 6

Bake until the sandwich is heated through and the cheese melts, about 20 minutes. Uncover and bake until the rolls are lightly browned, 7 to 8 minutes. Transfer the slab to a cutting board, then cut into individual sliders with a serrated knife before serving.