Step 1

Place 1 stick unsalted butter in a small bowl and let sit at room temperature until softened.

Step 2

Arrange a rack in the middle of the oven and heat the oven to 425ºF. Line a baking sheet with parchment paper or aluminum foil.

Step 3

Cut 1 loaf Italian bread in half horizontally with a serrated knife. Halve each piece crosswise for a total of 4 pieces. Place the pieces cut-side up on the baking sheet.

Step 4

Thinly slice 2 medium scallions. Reserve 1 tablespoon of the dark green parts for garnish, then add the remaining to the bowl of butter. Mince 5 garlic cloves and add to the bowl of butter.

Step 5

Add 2 tablespoons mayonnaise, 1/2 teaspoon garlic powder, 1/2 teaspoon black pepper, 1/2 teaspoon granulated sugar, and 1/4 teaspoon kosher salt to the butter. Smash and stir together until combined into a spreadable paste. Spread the garlic butter evenly onto the cut side of the bread.

Step 6

Grate 3 ounces low-moisture mozzarella cheese on the large holes of a box grater (about 1 cup). Grate 3 ounces Parmesan cheese on the small holes of a box grater (about 1 cup). Place both cheeses in a medium bowl and toss to combine. Sprinkle the cheeses evenly over the garlic bread.

Step 7

Bake until the cheese is melted and browned in spots, about 15 minutes. Garnish with the reserved scallions.