7 tablespoons unsalted butter, plus more for the dish
Kosher salt
1 pound elbow macaroni
1 small onion, finely chopped
2 stalks celery, finely chopped
3 cups shredded rotisserie chicken
2 cloves garlic, minced
3/4 cup hot sauce (preferably Frank's)
2 tablespoons all-purpose flour
2 teaspoons dry mustard
2 1/2 cups half-and-half
1 pound yellow sharp cheddar cheese, cut into 1-inch cubes (about 3 1/2 cups)
8 ounces pepper jack cheese, shredded (about 2 cups)
2/3 cup sour cream
1 cup panko (Japanese breadcrumbs)
1/2 cup crumbled blue cheese
2 tablespoons chopped fresh parsley