Adjust oven rack to middle position, place rimmed baking sheet on rack, and heat oven to 425 degrees. Using fork, beat butter, garlic, sugar, and pepper in a small bowl until combined. Spread butter mixture evenly over both sides of bread. Sprinkle with Parmesan cheese (optional) on one side of the bread (top side). Arrange buttered bread on heated baking sheet and bake until golden brown on first side, 8-10 minutes. Flip and bake until golden brown on second side, about 4-5 minutes.