2 (7 oz.) cans solid white tuna, drained
3 tbsp. mayonnaise
3 tbsp. commercial sour cream
1 very sm. onion, sliced paper thin and separated into rings
3 med. (about 1 lb.) potatoes, cooked, peeled, mashed
3/4 c. (3 oz.) Cheddar cheese, grated med. fine and packed down

Flake the tuna and stir in the mayonnaise, sour cream and onion. Spread over the bottom of an ungreased 9-inch pie plate; top with potatoes. Sprinkle with the cheese. Bake in a preheated 375 degree oven until hot through and cheese melts, about 15 minutes. Let stand 5 minutes or so before cutting into wedges. Serves 4-6.