Preheat the oven to 350°F (175°C). Grease a 9×13-inch baking pan.
In a large mixing bowl, cream together the butter and granulated sugar until light and fluffy.
Beat in the eggs, one at a time, then stir in the vanilla extract.
Combine the flour, baking powder, baking soda, and salt; gradually add to the wet ingredients.
Fold in the sour cream until well combined.
Spread half of the batter into the prepared pan.
In a small bowl, mix the brown sugar and cinnamon. Sprinkle half of this mixture over the batter in the pan.
Drop remaining batter in small spoonfuls over the brown sugar layer and spread carefully.
Sprinkle the remaining brown sugar mixture on top.
Using a knife, swirl the brown sugar layer into the batter.
Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
Allow the cake to cool slightly before serving.