Preheat oven to 350°F (175°C) and grease a 9-inch cake pan.
In a bowl, whisk flour, baking powder, baking soda, and salt.
In another bowl, beat butter and sugar until creamy. Add eggs and vanilla, mix well.
Add the dry ingredients to the wet ingredients, alternating with sour cream. Gently fold in the blueberries.
Pour batter into the pan.
In a separate bowl, mix the streusel topping ingredients until crumbly.
Sprinkle the streusel over the top of the cake batter.
Bake for 40-45 minutes, or until a toothpick comes out clean.
Let cool before serving.