Combine butter, parsley, Pecorino Romano cheese, and garlic in a small bowl.
STEP 3
Lightly coat 1 side of each bread slice with butter mixture; flip. Top 2 bread slices with provolone and mozzarella cheese; place remaining 2 bread slices, buttered-sides up on top.
STEP 4
Cook until golden brown on one side, 3 to 4 minutes. Flip; cook until cheese melted and golden brown on second side, 3 to 4 minutes more. Cut sandwiches in half; serve.