Place the bottom half into a 9x12 baking dish and spread with 1/2 of the mayonnaise.
Slice ham very thin.
Divide ham over bottom half.
Divide cheese over bottom half.
Spread mayonnaise on the inside of the top buns and place on top of the ham and cheese on the bottom buns.
In a small saucepan on low, melt the butter and then remove from heat.
Whisk in the mustard, onion flakes, Worcestershire and poppy seeds.
With a basting brush, brush sauce over tops of rolls.
Cover with foil and let sit on the counter for at least 30 minutes, or overnight in the refrigerator.
Bake at 350 degrees for 15 minutes, or until cheese is melted.
Uncover and sprinkle the brown sugar over the top and place back in oven for 5 more minutes, or until the top buns are slightly brown. Serve warm.
This can be prepared the prior day. After covering the buns, place in refrigerator overnight and then allow to come to room temperature for 30 minutes before baking.The Southern Baked Ham Buns are best made with real ham cut from a ham like in my Instant Pot Maple Glazed Ham recipe, as opposed to using pre-sliced packaged ham, which is most likely processed ham. However, if you are in a crunch, you can use the packaged ham, but you will note the flavor difference in using real ham. Make sure to squeeze out the excess water from the processed stuff.