The flavor! And cheese!!
For each sandwich:
2 slices bread
2-3 T butter/margarine
1 T finely chopped red onion
2-3 T mini pepperoni slices
4 slices mozzarella cheese
Butter outsides of bread. Lay one slice of bread down on 350°F preheated griddle. Lay two slices of cheese on bread. Follow with onion, pepperoni and remaining slices of cheese. Top with other slice of bread, butter facing out. Cook each side until golden, 5 minutes or so each.