In a small bowl, mix together 2½ teaspoons of ground cinnamon, 2 tablespoons of brown sugar, and ¼ cup of granulated sugar. Stir until well combined, and set aside for later use.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 1 cup of granulated sugar, 1 teaspoon of baking soda, and ½ teaspoon of salt. Set this bowl aside.

In a medium bowl, combine 1 cup of buttermilk, 1 egg, and ¼ cup of canola oil. Optionally add butter extract. Whisk until smooth and gently fold into the dry ingredients.

Pour half of the prepared batter into a greased loaf pan, spread it evenly, then sprinkle ⅔ of the cinnamon sugar mixture over it. Top with remaining batter.

Gently swirl the remaining cinnamon sugar mixture into the top layer of batter using a knife.

Preheat oven to 350°F and bake for 50-60 minutes. Check for doneness with a toothpick.

Allow the loaf to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely for at least 20 minutes.

In a small bowl, whisk together 1 cup of confectioners' sugar and milk until smooth for the glaze. Drizzle over the cooled loaf.