Tuna And Potato Casserole
["4 c. thinly sliced potatoes", "3 Tbsp. butter or margarine", "1/4 c. flour", "2 Tbsp. prepared mustard", "2 c. milk", "1 tsp. salt", "1/8 tsp. pepper", "1 (7 oz.) can tuna, flaked (1 c.)", "1 c. thinly sliced, peeled onion"]
["Cook potatoes in boiling salted water 10 minutes.", "Drain, melt butter in top of double boiler over direct heat.", "Stir in flour, then mustard.", "Add milk, salt and pepper and stir over boiling water until smooth and thick.", "Arrange potatoes, tuna and onions in alternate layers in a greased 2-quart casserole dish (I make 2 layers each; can add other can of tuna for richer dish).", "Pour sauce over all and bake for 45 minutes."]
["potatoes", "butter", "flour", "mustard", "milk", "salt", "pepper", "tuna", "onion"]