In a small bowl, mix the softened butter, garlic powder, and Italian seasoning. Spread the butter mixture evenly on one side of each slice of bread.

Place two slices of bread butter-side down on a cutting board. Spread a thin layer of pizza sauce on the unbuttered side. Sprinkle half of the shredded mozzarella and Parmesan cheese over the sauce. Add a layer of pepperoni slices, then top with the remaining cheese.

Place the remaining bread slices on top, butter-side up.

Heat a skillet or griddle over medium heat. Place the sandwiches in the skillet and cook for 3-4 minutes per side until golden brown and crispy, and the cheese is melted.

Remove from the skillet, let cool slightly, and serve with extra pizza sauce for dipping.