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 minute. Cut bananas in half lengthwise and crosswise creating 4 half slices each. Add banana slices, cut sides down, and peanuts to skillet. Cook 1 minute or until bananas are evenly coated and tender, basting occasionally with sauce. Spoon bananas into 4 dessert dishes; top with remaning sauce from skillet. Drizzle chocolate on top of bananas. Top with whipped topping.