Preheat the 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 ground cinnamon. Set aside.

In a large bowl, cream the softened butter and granulated sugar together 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 butter mixture, alternating with the buttermilk. Begin and end with the dry ingredients, mixing until just combined.

In a small bowl, mix the brown sugar and ground cinnamon for the swirl.

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

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

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