Potato Puff Casserole 27 Nov 12

1 small onion, chopped
2 tablespoons butter
1/2 cup milk
1/2 tsp ground mustard
1/4 tsp salt
1/8 tsp pepper
2 cups mashed potatoes (prepared with milk and butter)
2 eggs, separated
1 cup shredded cheddar cheese

In skillet, saute onion in butter. Stir in milk, mustard, salt and pepper and bring to a boil. Remove from the heat; stir in potatoes and mix well. Stir in egg yolks until smooth. Cool at room temperature for 15 minutes. Stir in cheese. In a small mixing bowl, beat egg yolks until soft peaks form. Fold into potato mixture. Spoon into greased 1 quart baking dish. Bake at 350 degrees for 40-45 minutes or until lightly browned.