01 - Lay out all bread slices on a clean work surface. Spread approximately 1/2 tablespoon of softened butter evenly on one side of each slice.
02 - On the unbuttered side of two bread slices, spread 1 1/2 tablespoons of basil pesto in an even layer to the edges.
03 - Layer sliced mozzarella and provolone over the pesto-coated slices. Add tomato slices if desired, sprinkle with grated Parmesan, and season with freshly ground black pepper.
04 - Top each prepared slice with the remaining bread slices, ensuring the buttered sides face outward for optimal crisping.
05 - Heat a large nonstick skillet or griddle over medium-low heat until evenly warmed.
06 - Place sandwiches in the preheated skillet. Cook for 3-4 minutes per side, pressing gently with a spatula, until bread achieves golden-brown color and cheese is completely melted.
07 - Remove sandwiches from skillet and allow to rest for 1-2 minutes. Slice diagonally and serve warm while cheese remains gooey.