01 - Evenly spread softened unsalted butter on one side of each bread slice.
02 - Place two bread slices, buttered side down, onto a clean work surface.
03 - Drizzle extra virgin olive oil over the exposed, unbuttered sides. Layer mozzarella slices, followed by tomato slices and fresh basil leaves. Season generously with salt and freshly ground black pepper.
04 - Lightly drizzle balsamic glaze over the tomatoes.
05 - Place the remaining two bread slices on top, buttered side facing up.
06 - Warm a nonstick skillet or grill pan over medium heat.
07 - Carefully transfer the sandwiches into the preheated pan. Cook for 3 to 4 minutes per side, gently pressing with a spatula, until the bread is golden brown and the cheese is thoroughly melted.
08 - Remove sandwiches from the pan and let rest for one minute. Slice and serve immediately while hot.