01 - Spread softened butter evenly on one side of each bread slice.
02 - Place two bread slices, buttered side facing down, on a clean surface.
03 - Spread 2 tablespoons marinara sauce evenly across the unbuttered side of each base slice.
04 - Divide mozzarella cheese between the two slices, layering evenly. Arrange pepperoni slices over the cheese.
05 - Sprinkle each sandwich with grated Parmesan, dried oregano, and red pepper flakes if desired. Top with remaining bread slices, ensuring buttered sides face outward.
06 - Heat a large skillet over medium heat. Place sandwiches into the pan and cook for 3 to 4 minutes on each side, pressing gently, until bread is golden and cheese is melted.
07 - Transfer sandwiches to a cutting board, allow to cool slightly, then slice in half. Serve immediately with extra marinara sauce in a small bowl for dipping.