Preheat oven to 350 degrees and spray a 9x5 baking pan with pam baking spray.
Using a large bowl, whisk together the flour, baking powder, baking soda and salt.
Using a large bowl, beat the butter and sugar with a hand mixer until light and fluffy.
Beat in the eggs and sour cream until combined.
Gradually beat in the dry ingredients until combined and smooth.
Fold in the blueberries until combined.
Pour the batter into the baking dish and smooth evenly and set aside.
Using a medium bowl, whisk together the flour, sugar, walnuts, and cinnamon until combined.
Using your fingers, crumble the butter into the dry ingredients to create a crumble.
Sprinkle onto the top of the batter.
Place the cake into the oven and bake for 30-40 minutes or until a toothpick comes out clean.
Allow to cool completely before serving.