Melt butter in small sauce pan. Add minced onion and cook about 3-4 minutes until onions are translucent. Add next 3 ingredients. Let cool slightly. Slice party rolls with out seperating into individual rolls. Place on a large sheet of foil. Spread the bottom 1/2 of rolls with 1/2 of sauce, layer ham then cheese and top with the other 1/2 of roll. Wrap in foil.
Bake 15 minutes. Cool and few minutes then slice through the rolls to seperate into 12 rolls each.