Microwave potatoes 1 inch apart on paper towels at HIGH 12 minutes or until done, turning and rearranging after 5 minutes; cool, peel, and mash.
Stir together potatoes and next 7 ingredients; spoon into a shallow 2-quart casserole coated with cooking spray.
Bake at 350° for 30 minutes or until a knife inserted in center comes out clean. Garnish, if desired.
*2 (14 1/2-ounce) cans mashed sweet potatoes may be substituted.