01 - Lay out bread slices on a clean work surface. Spread 1/2 tablespoon softened butter evenly on one side of each slice.
02 - Spread 1 1/2 tablespoons basil pesto on the unbuttered side of two bread slices.
03 - Layer mozzarella and provolone over the pesto. Add tomato slices and Parmesan if desired. Season with black pepper. Top with remaining bread slices, buttered side facing outward.
04 - Heat a large nonstick skillet or griddle over medium-low heat.
05 - Place sandwiches in the skillet. Cook for 3-4 minutes per side, pressing gently with a spatula, until bread is golden brown and cheese is completely melted.
06 - Remove from skillet and let rest for 1-2 minutes. Slice diagonally and serve warm.