Preheat oven to 325F degrees.
Peel potatoes and cut into cubes. Boil potatoes 15 mins. or until done. Drain and transfer potatoes into a large mixing bowl, add butter, salt, cream cheese, sour cream, milk.
Mix with hand mixer until blended together. Add chopped onion, cheese and stir.
Place in oven-safe casserole dish and bake at 325 degrees for 35-40 minutes.
Submitted by: J.B.