01 -
Preheat the oven to 350°F. Lightly grease a 9x13-inch baking dish or line it with parchment.
02 -
Keep the rolls attached and slice the whole slab in half horizontally with a serrated knife. Place the bottom half in the prepared dish.
03 -
Spread the bottom rolls with mayonnaise. Layer the ham evenly over the rolls, then add the Swiss cheese in an even layer. Set the top half of the rolls back in place.
04 -
In a small bowl, stir together melted butter, Dijon mustard, Worcestershire sauce, poppy seeds, dried onion, garlic powder, and salt.
05 -
Brush the butter mixture evenly over the tops and edges of the rolls. Let the tray sit for 5 minutes while the topping settles into the seams.
06 -
Cover the dish with foil and bake for 15 minutes, until the cheese is melted and the centers are hot.
07 -
Remove the foil and bake for 5 more minutes, until the tops are glossy and lightly golden. Rest for 5 minutes, sprinkle with parsley if using, then cut into 12 sliders.