Preheat the oven to 350 F. Cook the pasta according to package directions, drain. Melt the butter in a large saucepan over medium heat. Cook the garlic in the butter until fragrant.
Add in flour, mix for a minute until browned. Pour in milk, 1 cup shredded mozzarella cheese, grated parmesan cheese, salt, and pepper. Continue to cookie while whisking, until the cheese has completely melted and the sauce has thickened.
Mix the sauce with the pasta. Spread it into a greased baking dish. Top with the remaining 1 cup shredded mozzarella cheese. Top with french fried onions. Bake for 20-25 minutes.