Combine all sauce ingredients and set aside. Sauce may be made 24 hours in advance and refrigerated until needed
To prepare the French bread:
Adjust the oven rack to an upper-middle position. Preheat oven to 450°F.
Using a serrated knife, cut the bread in half crosswise. Cut each half lengthwise to create 4 equal pizza crusts. Place the bread, cut side up on a large rimmed baking sheet.
In a small bowl, combine the butter, granulated garlic, salt and red pepper flakes. Cover and microwave until melted, about 40 seconds. Stir to combine then brush the butter mixture on the cut side of bread.
Bake in the preheated oven until well browned around the edges, about 5 minutes.
Remove from the oven and spread the sauce evenly over the toasted bread. Top with mozzarella then Parmesan. Add additional toppings as desired.
Bake until the cheese is melted, about 15 minutes. Cool for 5 minutes then serve.
Sauce is easily doubled and also freezes well. It's great for dipping, too!