Preheat the oven to 350°F. In a large bowl, whisk together the flour, 1 cup sugar, the baking soda and salt. In a separate bowl, whisk together the buttermilk, egg and oil until very well combined. Using a rubber spatula, stir the wet ingredients into the dry ingredients just until moistened. Editor’s Tip: Be careful not to overmix the batter once the wet and dry ingredients are combined. Overmixing will cause an over-development of gluten, resulting in a tough, dense bread.
In a small bowl, whisk together the cinnamon and remaining ½ cup sugar until everything is evenly distributed.
Grease only the bottom of a 9x5-inch loaf pan. Pour half the batter into the pan and gently spread it out evenly to all four corners. Sprinkle the top with half the cinnamon sugar. Pour the remaining batter on top and carefully spread it out. Sprinkle the top with the remaining cinnamon sugar. Using a butter knife, cut through the batter a few times to create a swirl.
Bake the loaf until a toothpick inserted in the center comes out clean, 45 to 50 minutes. Cool the loaf for 10 minutes at room temperature. Remove the loaf from the pan and onto a wire rack to cool completely to room temperature.
In a small bowl, whisk together the confectioners' sugar and just enough milk to reach the desired consistency. Drizzle the glaze over the loaf.
