Butter one side of each bread slice. Place two slices, buttered side down, on a cutting board.
Spread pizza sauce on the unbuttered side of each. Sprinkle with mozzarella, then layer on pepperoni, a dusting of Parmesan, and Italian seasoning.
Top with the remaining bread, buttered side facing out.
Heat a nonstick skillet over medium heat. Cook sandwiches 3–4 minutes per side until golden brown and cheese is melted.
Slice and serve with extra pizza sauce for dipping!