Preheat your oven to 350°F (175°C) and prepare a 9x5-inch loaf pan by greasing it thoroughly.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and ground cinnamon.

In a large bowl, cream together the unsalted butter and granulated sugar until light and fluffy, about 3-4 minutes.

Gradually add in the eggs one at a time, mixing well after each, then stir in the vanilla extract.

Gradually add the dry ingredient mixture to the butter and sugar blend, alternating with sour cream.

Pour half of the batter into the prepared loaf pan, sprinkle half of the cinnamon sugar mixture over the batter.

Pour the remaining batter into the pan and sprinkle the leftover cinnamon sugar mixture on top.

Bake for 50-60 minutes, or until a toothpick inserted in the center comes out clean.

Let the loaf cool in the pan for about 10 minutes before transferring to a wire rack.