Preheat oven to 375.

cook noodles according to package directions, rinse and set aside.

In small saucepan, melt 3 TB of butter and cook onion until tender, then mix in flour to make a roux. Add salt, pepper, and mustard mixing until bubbling. Add milk all at once and bring to a boil, simmer until thick.

In large bowl, combine noodles, celery, tuna, sauce and cheese. Pour into a greased 9x13 casserole dish.

In a small bowl, melt remaining butter. add bread crumbs, then Portage over top of casserole.

cook in preheated oven for 25-30 minutes.