In a large bowl, combine the flour, 1/2 cup sugar, baking powder, salt, baking soda and caraway seeds. In another bowl, beat the egg, buttermilk, butter and oil. Stir into dry ingredients just until moistened. Fold in currants. , Fill greased muffin cups three-fourths full. Sprinkle with remaining sugar. Bake at 400° for 15 minutes or until a toothpick inserted in the center comes out clean. Cool for 5 minutes before removing from pan to wire rack. Serve warm.