Preheat the oven to 350°F (175°C). Grease and flour a bundt pan.
In a bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, cream the butter and sugar until light and fluffy.
Add the eggs one at a time, beating well after each. Mix in vanilla extract.
Alternate adding the dry ingredients and sour cream to the butter mixture, starting and ending with dry ingredients. Add milk and mix just until combined.
In a small bowl, stir together the brown sugar and cinnamon for the swirl.
Pour half of the batter into the bundt pan. Sprinkle cinnamon-sugar mixture evenly. Top with remaining batter and swirl lightly with a knife.
Bake for 50–60 minutes or until a toothpick inserted comes out clean.
Let the cake cool in the pan for 15 minutes, then invert onto a wire rack to cool completely before serving.