1. Prepare the Crust:

1. Preheat oven to 350°F (175°C). Grease a 9-inch round cake pan.
2. In a large bowl, cream together butter and granulated sugar until light and fluffy.
3. Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.
4. In a separate bowl, whisk together flour, baking powder, and salt.
5. Alternately add the flour mixture and milk to the butter mixture, beginning and ending with the flour.
6. In a small bowl, mix cinnamon and brown sugar for the swirl.
7. Pour half the batter into the prepared pan. Sprinkle half the cinnamon-sugar mixture over the batter. Repeat with remaining batter and cinnamon-sugar.
8. Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
9. Let cool in the pan for 10 minutes before transferring to a wire rack.