MELT butter in large skillet on medium heat. Add sugar; cook until melted, stirring occasionally. Reduce heat to low. Gradually add sour cream; cook 1 min.
CUT bananas in half lengthwise and crosswise creating 4 half slices each. Add banana slices, cut sides down, and peanuts to skillet. Cook 1 min. or until bananas are evenly coated and tender, basting occasionally with sauce.
SPOON bananas evenly into 4 dessert dishes; top with remaining sauce in skillet. Drizzle chocolate on top of bananas. Top each evenly with whipped topping.