Preheat the oven to 350 degrees F. Position a rack over a baking sheet.
Melt the butter with the garlic in a small saucepan over medium-low heat. Brush both sides of the muffins with the garlic butter and place them split-side up on the rack. Sprinkle with the Parmesan. Bake until browned, about 10 minutes. Serve immediately.