Begin by preheating your oven to 350°F (175°C). Grease a 9x5-inch loaf pan with butter or non-stick spray.

Combine 2 cups of all-purpose flour, 2 teaspoons of baking powder, 1 teaspoon of baking soda, 1 teaspoon of salt, and 2 teaspoons of ground cinnamon in a bowl. Whisk until evenly distributed.

In a large bowl, beat ½ cup of softened unsalted butter, ¾ cup of granulated sugar, and ¾ cup of brown sugar together until light and fluffy.

Add 2 large eggs one at a time, beating well after each. This will help bind the ingredients.

Stir in ½ cup of buttermilk and 1 teaspoon of vanilla extract until well combined.

Gradually add the dry mixture to the wet ingredients in two batches, alternating with the remaining ½ cup of buttermilk.

In a small bowl, mix ¼ cup of granulated sugar and 2 teaspoons of ground cinnamon. In the loaf pan, layer half of the batter, sprinkle with half of the cinnamon sugar mixture, and gently swirl with a knife.

Repeat layering with the remaining batter and cinnamon topping.

Bake the loaf for 50-60 minutes or until a toothpick inserted comes out clean or with a few moist crumbs.

Cool in the pan for about 10 minutes before transferring to a wire rack to cool completely.

For an optional glaze, mix 1 cup of powdered sugar with 2 tablespoons of milk until smooth, then drizzle over the cooled loaf.