HEAT oven to 350ºF.
COMBINE flour, 1/2 cup sugar, baking powder, baking soda and salt; set aside. Mix egg, bananas, sour cream and oil in large bowl. Add dry ingredients; stir just until moistened. (Batter will be lumpy.)
SPOON into 12 paper-lined muffin cups. Mix remaining sugar and cinnamon; sprinkle over batter.
BAKE 22 to 24 min. or until toothpick inserted in centers comes out clean. Cool in pan 5 min. Remove to wire racks; cool.