In a medium-sized bowl, combine the softened unsalted butter, grated parmesan cheese, garlic powder, and Italian seasoning. Mix until the mixture is smooth and well combined.

Spread the garlic butter mixture evenly over one side of each slice of bread. Place the bread slices on a sheet tray with the buttered side facing up until you are ready to assemble.

Heat a skillet over medium-low heat. Place one slice of bread into the skillet with the buttered side facing down.

Begin layering the sandwich by placing one slice of mozzarella cheese on the bread. Add 6 pepperoni slices, followed by another slice of mozzarella, 6 more pepperoni slices, and a final slice of mozzarella cheese.

Place a second piece of bread on top with the buttered side facing up.

Cover the skillet with a lid to help the cheese melt thoroughly. Cook for approximately 3 to 5 minutes or until the bottom slice of bread is a perfect golden brown.

Carefully flip the sandwich using a spatula. Replace the lid and continue cooking the other side until it is golden brown and the cheese in the center is fully melted.

Repeat the process for the remaining sandwiches and serve immediately with a side of warm pizza sauce for dipping.