Buffalo-Chicken Macaroni and Cheese

INGREDIENTS

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