In a small sauce pan, melt unsalted butter then saute onion for about a minute over medium heat. Add garlic powder, Dijon mustard, brown sugar, Worcestershire sauce and poppy seeds. Simmer for another minute then remove from the stove.
Lay rolls on a flat surface and slice with a serrated knife. Transfer and arrange the bottom half of rolls in a greased oven safe tray or baking pan then spread the mayonnaise and brush the rolls with butter sauce.
Add the rolled ham and cheese then brush the top with butter sauce. Note: Spread around the extra ham and cheese.
Before adding the other half of rolls, brush the inside with butter sauce then the top of rolls and pour remaining sauce on the sides.
Cover with foil and refrigerate for half a day or overnight.
Bake for 20 minutes covered and 5 minutes uncovered for a total of 25 minutes.
Let it sit for a couple of minutes then separate rolls with spatula or knife. Serve warm.
Notes
You can prepare the sliders in the baking pan ahead of time, cover with foil and store in refrigerator up to 2 days.
Reheat leftovers or serve it cold.
STORING LEFTOVERS: Store leftovers in an airtight container up to 3 days. You can make extra servings and freeze it. If you are using a zip lock bag, I suggest to place sliders in a single layer with the card board that came with the rolls. It is easier to store it with the card board.
COOKING IN AIR FRYER: Aside from baking sliders, you can also use an air fryer. I have a Gourmia 7 QT/6.7 and can fit about 6 sliders. Temperature is set to 300 degrees F for 5-6 minutes. I did not set PRE-HEAT and did not TURN the sliders.
REHEATING SLIDERS:Oven – If stored in the refrigerator, place sliders in baking pan and cover with foil. Pre-heat oven at 325 degrees F and reheat for 10 minutes or until warm. If frozen, thaw fully in the refrigerator before reheating. Air Fryer – If stored in the refrigerator, do not pre-heat, set air fryer temperature at 300 degrees F for 2 minutes. If frozen, pre-heat at 300 degrees F for 2-3 minutes. Tip:If frozen, it is better to reheat with top of roll off. You get a crispier roll and ham is well heated.