Buffalo Chicken Mac and Cheese

I made this last summer for a birthday party and it was really delicious! Not as time consuming as it seems below, especially if you have helpers in the kitchen. Definitely worth it, everyone loved the spicy-cheesiness. Can be prepared 2 hours ahead. 
 
1 pound cooked chicken, seasoned with salt and pepper then drenched in Frank's Hot Sauce

1 pound small elbow macaroni
8 tablespoons (1 stick) butter, divided
3 cups chopped onions
2 large garlic cloves, chopped
1/2 cup all purpose flour
4 cups whole milk
1 pound extra-sharp cheddar cheese, coarsely grated (about 4 cups packed)
8 ounces provolone cheese, coarsely grated (about 2 cups packed)
2 teaspoons paprika
salt and black pepper
Yield: Makes 12 servings

Cut chicken into into 1-inch-long bite sized strips.

Cook macaroni in large pot of boiling salted water until just tender but still firm to bite. Drain; transfer to very large bowl.

Melt 6 tablespoons butter in same large pot over medium heat. Add 3 cups chopped onions and garlic. Cover; saute until onions are soft but not brown, stirring often, about 6 minutes. Add flour; stir 2 minutes. Gradually whisk in milk. Bring to boil, whisking constantly. Reduce heat and simmer sauce 2 minutes. Add all cheeses, paprika, 1 teaspoon salt, and 1 teaspoon pepper. Whisk until cheeses melt and sauce is smooth, about 2 minutes. Remove from heat. Mix cheese sauce into macaroni. Mix in chicken pieces. Mound mixture in 13x9x2-inch glass baking dish. Let stand at room temperature.

Preheat oven to 350 F. Stir in hot sauce and remaining 2 tablespoons butter in small saucepan over medium heat until butter melts; spoon 4 tablespoons over macaroni in dish. Bake macaroni uncovered until heated through, about 30 minutes, or 45 minutes if made ahead. Serve, passing remaining butter and hot-sauce mixture separately.