4 c. sliced potatoes, cooked in salted water 10 minutes
3 T. butter or margarine
1/4 c. flour
1 3/4 c. milk
1 t. salt
1/8 t. pepper
2 T. mustard
1 c. sliced onions
1 can (6 oz.) tuna, drained
Bread crumbs - optional
Cook potatoes, drain and set aside.
PREPARE SAUCE: In saucepan, over medium heat, melt butter; stir in flour; cook 2 minutes, stirring until smooth.
Add milk gradually while stirring. Blend in salt, pepper and mustard.
Layer potatoes, onions and tuna in greased 2-qt. casserole with sauce.
Top with bread crumbs, if desired.
Bake in preheated 375* F. 45 minutes.