Pre-heat oven to 350º.
In a large bowl, combine flour, 1 C sugar, baking soda and salt.
Combine buttermilk, egg and oil, stir into dry ingredients just until moistened.
In a small bowl, combine cinnamon and remaining sugar.
Grease the bottom only of a 9 x 5" loaf pan.
Pour half the batter into pan; sprinkle with half the cinnamon mix.
Carefully spread with remaining batter and sprinkle with remaining cinnamon mix.
Cut through batter with a knife to swirl.
Bake 45-50 minutes or until toothpick inserted in center comes out clean.
Cool 10 minutes before removing from pan to a wire rack. Cool completely.
Combine powdered sugar and enough milk to reach desired consistency; drizzle over loaf.