| Heat oven to 350°. Coat a 3-quart broiler-safe baking dish with nonstick cooking spray. Bring a large pot of lightly salted water to boiling. Cook pasta 8 minutes in boiling water; drain. Meanwhile, in medium-size saucepan, cook bacon over medium heat, until crisp, approximately 6 minutes. Transfer to paper towels. Carefully pour off drippings, leaving 2 tablespoons in pan. Add butter. Whisk in flour until smooth. In a thin stream, whisk in milk. Stir in onion flakes, salt and pepper. Bring to a boil over medium-high heat, then reduce heat and simmer 2 minutes. In large bowl, toss together cheddar, colby-Jack and mozzarella. Remove milk mixture from heat; whisk in American cheese and 1 1/4 cup of the Cheddar mixture. Toss bacon pieces with remaining shredded cheese. In pasta pot, combine cooked pasta and cheese sauce. Pour half into prepared dish. Sprinkle with a generous cup of the bacon-cheese mixture. Repeat layering. Bake at 350° for 20 minutes. Increase oven temperature to broil and broil 3 minutes, until top is lightly browned. Cool slightly before serving. Garnish with green onions, if desired. | 
