How to Make It
Preheat broiler to high.
Remove white papery skin from garlic heads (do not peel or separate the cloves). Place garlic heads in a microwave-safe bowl; rub garlic heads with oil. Pour 3 tablespoons water into bottom of bowl. Cover with plastic wrap. Microwave at HIGH for 4 minutes and 30 seconds or until garlic is very tender; cool slightly.
Cook pasta according to package directions, omitting salt and fat; drain.
Combine milk and flour in a medium saucepan, stirring with a whisk. Bring to a boil over medium-high heat, stirring frequently. Cook 3 minutes or until thickened; remove from heat. Stir in salt, pepper, 1 ounce cheddar, and mozzarella.
Separate garlic cloves; squeeze to extract garlic pulp. Discard skins. Place garlic pulp and 2 cups milk mixture in a blender; process until smooth. Stir garlic mixture into milk mixture. Add pasta; stir to coat. Spoon pasta mixture into 6 (10-ounce) ramekins or gratin dishes or a broiler-safe 11 x 7-inch glass or ceramic baking dish coated with cooking spray. Sprinkle evenly with remaining 3 ounces cheddar. Broil 2 minutes or until cheese melts and begins to brown. Let stand 5 minutes.