Combine the flour, 1 cup sugar, baking soda and salt in a large bowl.
MIx together buttermilk, egg and oil and stir into flour mixture until blended.
Mix together cinnamon and 1/2 cup sugar in small bowl.
Spray the bottom of a loaf pan with cooking spray.
Pour half of the batter into pan then sprinkle 2/3 of the swirl mixture.
Pour remaining batter and sprinkle with remaining swirl mixture.
Take a knife or spatula and cut through batter to swirl.
Bake at 350 for 60-70 minutes or until a toothpick inserted comes out clean (cooking times vary a lot).
Cool for 10 minutes in pan then remove and place on wire rack.
Place powdered sugar in a bowl slowly add milk stiring until you get to syrup consistency, then drizzle over loaf.