Preheat your oven to 350°F (175°C). Grease and flour a 10-inch Bundt pan.

In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and 1 teaspoon of ground cinnamon. Set aside.

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

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk. Begin and end with the dry ingredients, mixing until just combined.

In a small bowl, mix together the brown sugar and 1 teaspoon of cinnamon for the swirl.

Pour half of the batter into the prepared Bundt pan. Sprinkle the cinnamon-sugar mixture evenly over the batter. Pour the remaining batter on top and gently swirl with a knife to create a marbled effect.

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

Allow the cake to cool in the pan for about 15 minutes before inverting it onto a wire rack to cool completely.