Preheat the oven to 350°F (175°C) and grease a 9-inch cake pan.
In a bowl, combine flour, baking powder, baking soda, and salt.
Cream butter and sugar until fluffy.
Add eggs one at a time, mixing well.
Stir in sour cream and vanilla.
Gradually mix in the dry ingredients until smooth.
Gently fold in the blueberries.
Pour half the batter into the cake pan.
Mix brown sugar, cinnamon, and melted butter for the swirl.
Spoon half the cinnamon mixture over the batter and swirl it in.
Add the remaining batter, then top with the rest of the swirl.
Bake for 40 minutes, or until a toothpick comes out clean.
Let cool before serving.