Preheat oven to 350 degrees. Butter a 1-quart baking dish.
Melt the butter in a medium-size saucepan over medium heat. Stir in the flour and cook 1 minute. Gradually whisk in the milk then garlic powder. Cook, stirring constantly, until lightly thickened to the consistency of cream. Whisk in the Gorgonzola and Fontina. Cook, whisking constantly, until the cheeses are melted. Season with nutmeg and salt and pepper to taste. Remove from heat.
Combine the cheese sauce and cooked pasta. Stir in the mozzarella and spoon into the prepared baking dish. Sprinkle with the Parmesan and buttered breadcrumbs and then the paprika.
Bake until bubbling and the top is browned, about 30 minutes. Serve immediately.