Heat oven to 350. Spray a 9" x 13" casserole dish w/ cooking spray. Cook macaroni as directed, drain. In small saucepan, cook chopped sausage over medium heat until done.
Place sausage in a bowl and set aside. In same pan, melt 1 tbsp butter over medium heat. Add breadcrumbs. Remove from heat. Stir in parmesan cheese. In another pan, melt 1 tbsp butter over medium heat. Saute onions and celery until soft. Transfer to a bowl.
In same pan, melt 1 tbsp butter over medium heat. Whisk in flour. Mix in paprika and mustard. Stir in milk. Bring to a boil. Add cheeses. Simmer, stirring for 10 mins. Season w/ salt and pepper. Transfer macaroni to baking dish. Toss in sausage. Stir in cheese mix. Sprinkle casserole w/ breadcrumbs. Bake 20 mins, or until crust is golden brown.