Mix Cinnamon Sugar:

In a small bowl, mix together 2 1/2 teaspoons cinnamon, 2 tablespoons brown sugar, and 1/4 cup granulated sugar; reserve.

Whisk Dry Ingredients:

In a large bowl, whisk 2 cups all purpose flour (250g), 1 cup granulated sugar (200g), 1 teaspoon baking soda, and 1/2 teaspoon salt; set aside.

Combine Wet and Dry:

In a medium bowl, combine 1 cup buttermilk, 1 egg, 1/4 cup canola oil (60ml), and 1 teaspoon butter extract (optional). Pour the wet mixture into the dry ingredients and stir until just combined; avoid overmixing.

Layer Batter and Swirl:

Coat a 9x5-inch loaf pan with nonstick spray. Add half the batter to the pan. Evenly distribute 2/3 of the cinnamon-sugar mixture over the batter. Cover with the remaining batter, then sprinkle the rest of the cinnamon-sugar on top. Use a knife to cut through the batter, creating a swirl effect. Bake right away for optimal rise.

Bake and Cool:

Bake at 350°F (175°C) for 50-60 minutes, or until a tester inserted in the center comes out clean or the top springs back when lightly pressed. Let cool on a wire rack for at least 20 minutes before slicing. Serve warm or at room temperature.

Make and Drizzle Glaze:

For the glaze: In a small bowl, whisk 1/2 cup confectioners' sugar (60g), 1-2 tablespoons milk, and 1/2 teaspoon vanilla extract until smooth. Adjust consistency with more sugar or milk as needed. Drizzle over the loaf while still warm or after cooling. Allow glaze to set.