Preheat the oven to 350 degrees F and butter a 9-by-13-inch baking dish. Bring a large pot of salted water to a boil; add the pasta and cook until al dente, about 7 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 more 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-and-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, blue cheese and parsley. Sprinkle over the macaroni and bake until bubbly, 30 to 40 minutes. Let rest 10 minutes before serving.
Photograph by Con Poulos
Courtesy of Food Network Magazine