Butter one side of 9 slices of bread, and place butter-side down on a baking sheet. Arrange cheese on each slice of bread. Spread butter on 9 remaining slices of bread, and place them buttered-side up on top of the cheese.
Bake in preheated oven for 6 to 8 minutes. Flip the sandwiches, and bake an additional 6 to 8 minutes, or until golden brown.