Grease & flour a standard loaf pan. Set it aside for now.
In your mixing bowl, combine the flour, baking soda, salt, 1 cup of the sugar, & 1/2 teaspoon of the cinnamon. Set this aside for now.
In a separate bowl, or right in your measuring cup, combine the buttermilk, extra virgin olive oil, egg, and a teaspoon of vanilla. Give it a quick whisking with a fork to break up the egg. Pour your liquid mixture into the dry ingredients.
Mix until combined, making sure to scrap the bowl with a rubber spatula to get everything mixed well.
In a small bowl, combine the remaining 1/2 cup sugar and 2 teaspoons of cinnamon. Stir those together. Set aside.
Pour half of the batter into the loaf pan. Sprinkle half of the cinnamon sugar over the batter.
Spoon the remaining batter evenly all over the layer of cinnamon sugar and then sprinkle with the other half.
Run a knife through the batter, zigzagging end to end and side to side several times to swirl.
Bake this for 55-65 minutes, or until it tests done in the center when tested with a toothpick.
Cool the bread in the pan for about 10 minutes, then remove to a rack to finish cooling.
In a small dish, whisk together the powdered sugar, vanilla extract, and milk.