PREHEAT oven to 375°F Mix sour cream, cheese, soup and onions in large bowl. Add potatoes; mix well.
SPOON into greased 13x9-inch baking dish.
BAKE 45 minutes.
Toss crumbs with butter; sprinkle over potato mixture. Bake an additional 15 minutes
Variation Southwest Style Easy Potato Bake
Prepare as directed, using KRAFT Mexican Style Shredded Cheese, adding 1 can (4 oz.) undrained chopped green chilies to the potato mixture and substituting 1 cup crushed tortilla chips for the crushed corn flakes.