In a bowl, combine the flour, 1 cup sugar, baking powder and salt. In another bowl, beat the egg, milk and oil. Stir into dry ingredients just until moistened. Fold in rhubarb.
Fill paper-lined muffin cups three-fourths full. Sprinkle with remaining sugar. Bake at 350° for 25-30 minutes or until a toothpick inserted in the center comes out clean. Cool for 5 minutes before removing from pan to a wire rack. Serve warm.