Preheat your oven to 350°F (175°C) and grease a bundt pan.

In a large bowl, cream together the softened butter and sugar until light and fluffy.

Add the eggs one at a time, beating well after each addition. Stir in the vanilla and sour cream.

In another bowl, whisk together the flour, baking powder, baking soda, and salt. Gradually add to the butter mixture, mixing until just combined.

In a small bowl, mix together the cinnamon and brown sugar.

Pour half of the batter into the prepared bundt pan, sprinkle with half of the cinnamon-sugar mixture, then add the remaining batter and top with the rest of the cinnamon-sugar mixture.

Use a knife to swirl the cinnamon mixture into the batter.

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

Allow to cool in the pan for 10 minutes, then invert onto a wire rack to cool completely.