To make the slider spread, stir together mayonnaise and 2 tablespoons Dijon mustard in a small bowl. Set aside.

Using a serrated bread knife, slice the slider buns in half to separate the tops from the bottoms. Place them, cut side up, on a baking sheet.

Preheat your oven's broiler to high with the rack in the second position down from the top (this should be about 6 inches from the broiler element). Broil the rolls on the cut-sides only for 1-2 minutes, until lightly toasted. Watch them closely and do not walk away from the oven, as they can burn quickly! Broiling times may vary by oven

Preheat the oven to 350 degrees F with the rack in the middle position. Lightly spray a glass or light-colored ceramic baking dish with cooking spray. (If using a pan with a darker interior, reduce the oven temperature to 325 degrees F.)

Place the bottom half of the toasted rolls in the prepared baking dish. Spread a little more than half of the Dijon-mayo mixture onto the rolls in the baking dish.

Assemble the sliders by layering the cheeses and meat in the following order: cheddar cheese, ham, white cheddar cheese. Spread the remaining Dijon-mayo onto toasted side of the top half of the rolls and place them over the white cheddar cheese layer.

In a small bowl, combine the melted butter, Worcestershire sauce, onion powder, and a pinch of salt (if using). Pour over the sliders, using a basting brush or pastry brush to distribute the butter evenly over the tops and sides. It's ok if some of the butter pools around the sliders in the baking dish.

Cover with foil and let stand for 5 minutes. Bake for 20 minutes, until the sliders are heated through and the cheese is melted. Remove the foil and continue baking for 5-10 minutes, until the tops of the rolls are golden and crispy. Watch them carefully during the last stage of baking so they don't get too dark.

Let the sliders stand for a few minutes and cut the rolls into individual servings. Serve hot with potato chips, fries, or your favorite sandwich sides.