Combine butter and Parmesan cheese in a small bowl.

Each slice of bread should have a generous amount of butter mixture spread on one side.

Slices of mozzarella and cheddar cheese are arranged on the bread's unbuttered side. The slices might need to be torn in order to fit. Sandwiches can be topped with the remaining bread slices.

A big skillet should be heated at medium/low. Sandwiches are added and browned for 1–2 minutes on each side, or until the cheese melts. To give the cheese a chance to melt, make sure the heat is kept low to medium. Pro tip: To hasten the melting of the cheese, cover the skillet with a cookie sheet!

Slice the grilled cheese in half, remove from the skillet, and serve right away.