Scalloped Tuna-Potato Casserole - cooking recipe

Ingredients

4 c. thinly sliced potatoes
3 Tbsp. margarine
1/4 c. flour
2 Tbsp. prepared mustard
2 c. milk
1 tsp. salt
1/8 tsp. pepper
1 sliced onion
1 (7 oz.) can tuna

Preparation

Cook potatoes in boiling, salted water for 10 minutes, then drain.