Melt butter in a small skillet over medium high heat. Add onion, mustard, Worcestershire sauce, poppy seeds and brown sugar. Allow to sauté for a few minutes, until onions are translucent and tender. Remove from the stove.
Do not separate rolls, simply remove the entire dozen from the packaging. Slice the whole thing in half horizontally, removing the tops and placing the bottoms on a foil-lined baking sheet.
Place a spoonful of sauce on each roll, making sure to reserve some for later.
Lay slices of ham overlapping as necessary, to cover the sheet of rolls. Do the same with the cheese, placing it on top of the ham. Place the top layer of rolls over the ham and cheese.
Slowly pour the remaining sauce right over the tops of these babies. Cover with aluminum foil and allow to sit for 10 minutes.
Bake at 350F or place on an outdoor grill over low heat, for 20 minutes, or until the cheese is melted.
Uncover and bake for another two minutes until the tops are slightly browned and crisp.
Remove from oven, cut into 12 sliders and serve immediately. Yumm!
I have tried making these with Canadian bacon instead of ham, French Swiss cheese, and country-style Dijon mustard. All three tweaks made these babies even better, as if it’s possible to improve on perfection.