Spread butter on one side of each slice of bread. This will help create a crispy, golden crust.

Place one slice of bread, buttered side down, on a clean surface. Spread a thin layer of pizza sauce on the unbuttered side.

Sprinkle mozzarella cheese on top of the sauce and layer 6 slices of pepperoni over the cheese.

Top with the second slice of bread, buttered side facing up. Repeat for the second sandwich.

Heat a skillet or griddle over medium heat. Place the sandwiches in the pan and cook for 3–4 minutes, until the bottom is golden brown.

Flip the sandwiches carefully and cook the other side for another 3–4 minutes, until the cheese is melted and the bread is crispy.

Remove from the skillet, slice in half, and serve hot.