2-1/2 lbs. white potatoes, peeled, boiled, and mashed
1/2 cup sour cream
4 oz cream cheese
1 tbsp butter
1 tsp onion salt or 1 small onion, chopped
grated cheddar cheese

Combine first 5 ingredients, beating until fluffy. Sprinkle cheese on top.

Bake at 350°F for 20 minutes. Serve.