01 -
Preheat oven to 350°F and grease a 9x13 inch baking pan.
02 -
Sift together the all-purpose flour, baking powder, baking soda, and salt in a medium bowl.
03 -
In a large mixing bowl, beat together granulated sugar and unsalted butter until the mixture is light and fluffy.
04 -
Incorporate eggs one at a time, mixing thoroughly after each addition, then blend in vanilla extract.
05 -
Add the sifted dry ingredients alternately with the buttermilk, mixing gently until just combined.
06 -
Fold fresh blueberries evenly into the batter.
07 -
Spread the batter evenly in the prepared baking pan.
08 -
For the topping, combine flour and granulated sugar in a small bowl, then cut in softened butter until the mixture resembles coarse crumbs.
09 -
Sprinkle the crumble topping evenly over the batter.
10 -
Bake for 45 to 60 minutes, or until a toothpick inserted in the center comes out clean.
11 -
Cool in the pan before slicing and serving.