Shrimp Au Gratin

Directions

1. Melt butter, saute onion; add flour, salt, mustard, pepper and cook until bubbly, stirring constantly.
2. Add milk until bubbly, 3/4 cup of the cheese; stir until melted. Add shrimp and mushrooms.
3. Put in buttered casserole or individual shells; combine crumbs and 1/4 cup cheese; sprinkle over top and dot with butter.
4. Bake at 400 degrees F for 10 minutes.