Preheat the oven to 350°. Grease the bottom only of a 9x5-in. loaf pan.
In a large bowl, combine flour, 1 cup 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.
Pour half the batter into the pan and sprinkle with half the cinnamon-sugar.
Add the remaining batter and sprinkle with remaining cinnamon-sugar; cut through batter with a knife to swirl.
Bake for 45-50 minutes or until a toothpick inserted in the center comes out clean.
Cool 10 minutes before removing from the pan to a wire rack to cool completely.
To a small bowl, combine confectioners' sugar and milk. Drizzle over loaf.