Toss cheeses together in a bowl and set aside. Cook pasta according to pkg directions; drain well. Coat a 13- x 9-inch baking dish with vegetable cooking spray and add cooked pasta. Set aside. Melt butter in a large saucepan over medium heat.
Add garlic; cooking for 1 minute. Stir in flour, dry mustard and nutmeg. Gradually whisk in milk; making sure there are no lumps. Stir, bring to a boil; reduce heat and simmer for 1 minute. Remove from heat. Set aside 1 cup of tossed cheese.
Add remaining cheese to sauce one handful at a time, stirring until melted. Add herbs, salt and pepper to sauce and stir. Toss sauce with pasta. Sprinkle with reserved cheese. Place baking dish under broiler for about 1 minute or until cheese is bubbling.