1Heat broiler. Bring a large pot of lightly salted water to boiling. Add pasta and cook 8 minutes, or as stated on package directions; drain.
2Meanwhile, sprinkle chicken with 1/2 teaspoon of the celery seed, 1 teaspoon of the paprika and the salt. In a large skillet, heat oil over medium-high heat. Brown chicken, 3 to 5 minutes, until cooked through; set aside. Lower heat to medium. Add celery to same skillet; saute 4 minutes. Add garlic; continue cooking for 1 to 2 minutes more. Set aside with chicken.
3In saucepan, melt 3 tablespoons of the butter over medium heat. Sprinkle in flour and mustard powder, whisking for 2 minutes. Pour in milk and sauce, whisking until it boils. Simmer for 3 minutes. Remove from the heat; stir in cheddar, 1/2 cup of the blue cheese and remaing paprika.
4Add pasta, celery, garlic and chicken. Place in a broiler-safe dish.
5Microwave remaining tablespoon butter for 30 seconds. Stir in bread crumbs and remaining 1/2 teaspoon celery seed; sprinkle over dish with remaining 1/4 cup blue cheese. Broil for 2 to 3 minutes, or until browned.