1. Preheat your oven to 350°F. Generously grease and flour a Bundt pan to ensure the cake releases easily after baking.
2. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
3. In a large bowl, cream together the butter and granulated sugar using an electric mixer on medium speed until light and fluffy, about 3-4 minutes.
4. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
5. Gradually add the dry ingredients to the batter, alternating with the sour cream and milk. Begin and end with the dry ingredients, mixing just until combined.
6. In a small bowl, combine the cinnamon and brown sugar. This will be your cinnamon swirl.
7. Pour half of the batter into the prepared Bundt pan. Sprinkle the cinnamon-sugar mixture over the batter, then top with the remaining batter.
8. Using a knife, gently swirl the cinnamon mixture into the batter to create a marbled effect.
9. Bake in the preheated oven for 50-55 minutes, or until a toothpick inserted into the center comes out clean.
10. Allow the cake to cool in the pan for 15 minutes, then carefully invert it onto a wire rack to cool completely.

As you bake, remember Mama Lou’s advice: “Patience and love are the secret ingredients.” Let the cake cool completely before slicing to ensure it holds its beautiful shape.