2 large heirloom tomatoes (preferably Brandywine), cut into 1/4-inch slices
1/4 cup (1/2 stick) butter
Arrange 4 bread slices on work surface. Top bread with half of cheese slices (trimming to fit) and 2 tomato slices. Sprinkle tomatoes with salt and pepper. Top with remaining cheese, then remaining bread; press to compact.
Melt butter in large skillet over medium heat. Add sandwiches. Cover and cook until bread is golden, turning once, about 3 minutes per side.