In a large bowl, beat the butter, 1 cup sugar and egg until blended. Combine the flour, baking powder, baking soda and salt; add to egg mixture alternately with buttermilk. In a small bowl, combine the cinnamon and remaining sugar.
Pour a third of the batter into a greased 8x4-in. loaf pan; sprinkle with a third of the cinnamon sugar. Repeat layers twice. Bake at 350° for 45-50 minutes or until a toothpick inserted in the centre comes out clean. Cool for 10 minutes before removing from pan to a wire rack to cool completely.