Preheat oven to 350°F (175°C). Grease and flour a 9-inch pan.
In a bowl, mix flour, sugar, baking powder, baking soda, and salt.
In another bowl, beat together sour cream, egg, butter, and vanilla.
Combine the wet and dry ingredients until smooth.
Gently fold in fresh blueberries.
Pour the batter into the prepared pan.
In a small bowl, mix flour, brown sugar, cinnamon, and cold butter for the topping.
Sprinkle the crumb mixture evenly over the batter.
Bake for 35-40 minutes, or until a toothpick comes out clean.
Cool before serving.