Cut butter into potatoes. Mix rest of ingred. together; pour over top of potatoes. Toss.
*1/4 - 3/4 c. milk can be used in place of one-half of the sour cream. It will make a moister casserole, if desired.
Bake in a 13x9" pan @ 350 for 1/2 hr covered and an additional 1/2 hr. uncovered. I have used Cheddar Cheese soup, but reduce the butter as it will be greasy with both. I also put additional shredded cheese on top during the second half hour of baking. Doubles well. Can be refrigerated overnight after mixing all together.