Peel and cube potatoes. In a 4 quart dutch oven, cook potatoes in small amount of boiling salted water,covered, for 20 to 25 minutes or til tender. Drain and cool. Put in a large bowl. Beat with electric mixer on low speed. Add milk and butter. Beat til fluffy.
Preheat oven to 350. Beat cream cheese, sour cram,salt, pepper and garlic into potato mixture. Stir in onion. Transfer to a 2 quart round casserole. Top with cheese. Bake for about 30 minutes or until bubbly. Makes 8 to 10 servings.