Preheat oven to 350°F (175°C) and grease a 9-inch cake pan.
In a bowl, whisk together flour, baking powder, baking soda, and salt.
In another bowl, cream together butter and sugar until fluffy. Add eggs and vanilla, beat well.
Gradually add dry ingredients to the wet ingredients, alternating with sour cream.
Fold in the blueberries gently to avoid crushing them.
Pour the batter into the prepared pan.
In a separate bowl, mix the crumb topping ingredients until crumbly.
Sprinkle the crumbs evenly over the batter.
Bake for 35-40 minutes, or until a toothpick inserted comes out clean.
Let the cake cool before serving.