Ham & Swiss Sliders, Poppy Seed Butter

Method

1. Heat the oven to 350°F. Without pulling the rolls apart, slice each 12-roll slab in half horizontally with a long serrated knife, and set the bottoms in two 9x13-inch baking dishes.
2. Brush the cut bottoms with 2 tablespoons of the melted butter and bake 3 minutes, until the surface looks dry and set.
3. Layer half the Swiss over the bottoms, then the ham folded into loose ruffles, then the rest of the Swiss, and set the tops back on.
4. Whisk the remaining 6 tablespoons butter with the Dijon, Worcestershire, onion, poppy seeds and pepper, and brush it over the tops so some drips into the seams.
5. Cover tightly with foil. To make ahead, refrigerate up to 24 hours and bake from cold, adding 10 minutes.
6. Bake covered on racks in the upper and lower thirds for 15 minutes to melt the cheese, then uncover, swap the dishes and bake 8 to 10 minutes more, until the tops are deep golden and the cheese runs in the seams.
7. Rest 5 minutes, then cut along the seams and check that the centers read 165°F. Serve warm.