01 - Lay out bread slices on a clean work surface. Spread approximately 1/2 tablespoon softened butter evenly on one side of each slice.
02 - Spread 1 1/2 tablespoons basil pesto evenly on the unbuttered side of two bread slices.
03 - Layer mozzarella slices over the pesto, add provolone if using, then top with tomato slices and Parmesan cheese if desired. Season with freshly ground black pepper.
04 - Top each sandwich with remaining bread slices, ensuring buttered sides face outward.
05 - Preheat a large nonstick skillet or griddle over medium-low heat.
06 - Place sandwiches in the hot skillet and cook for 3 to 4 minutes per side, pressing gently with a spatula, until bread turns golden brown and cheese melts completely.
07 - Remove sandwiches from skillet and let rest for 1 to 2 minutes before slicing and serving warm.