Buffalo Chicken Mac n' Cheese

Buffalo Chicken Mac n' Cheese

1 pound corkscrew macaroni
1 small onion, finely chopped
2 stalks celery, finely chopped
3 cups shredded rotisserie chicken
2 cloves garlic, minced
3/4 cup Frank's red hot sauce
2 tablespoons flour
2 teaspoons dry mustard
2 1/2 cups half & half
1 pound yellow sharp cheddar cheese, cut into 1-inch cubes
1 cup pepper jack cheese, shredded
2/3 cup sour cream
1 cup panko breadcrumb
7 tablespoons unsalted butter, plus more for the dish
2 tablespoons chopped fresh parsley
Kosher salt

Preheat the oven to 350 degrees and butter a 9x13-inch baking dish. Bring a large pot of salted water to a boil; add the pasta and cook until al dente, about 9 minutes. Drain. Meanwhile, melt 3 tablespoons butter in a large skillet over medium heat. Add the onion and celery and cook until soft, about 5 minutes. Stir in the chicken and garlic and cook 2 minutes, then add 1/2 cup hot sauce and simmer until slightly thickened, about 1 minute.
Melt 2 tablespoons butter in a saucepan over medium heat. Stir in the flour and mustard with a wooden spoon until smooth. Whisk in the half & half, then add the remaining 1/4 cup hot sauce and stir until thick, about 2 minutes. Whisk in the cheddar and pepper jack cheeses, then whisk in the sour cream until smooth.
Spread half of the macaroni in the prepared baking dish, then top with the chicken mixture and the remaining macaroni. Pour the cheese sauce evenly on top.
Put the remaining 2 tablespoons butter in a medium microwave-safe bowl and microwave until melted. Stir in the panko and parsley. Sprinkle over the macaroni and bake until bubbly, 30 to 40 minutes. Let rest 10 minutes before serving.