Heat a large pan or griddle over medium heat
Butter one side of each slice of bread, and place in the pan, butter side down
Top each slice of bread with one slice of Fontina cheese, and cook until golden brown and the cheese has begun to melt
Repeat the process as needed until all bread is golden brown. Place all of the bread cheese side up on a sheet pan
Heat the pepperoni in the same pan until warm and the edges just begin to crisp
Place even amounts of pepperoni over 4 slices of bread, top each with one of the remaining bread slices, and press slightly before cutting in half
Serve immediately with a side of warm pizza sauce for dipping
Get creative with these sandwiches by adding other toppings like sautéed mushrooms, black olives, peppers and onions, or even something sweet like fig jam or hot honey!