01 -
Preheat oven to 375°F (190°C) and grease a 9x9-inch baking dish.
02 -
In a bowl, whisk together cake flour, baking powder, and salt.
03 -
In another bowl, beat the butter and sugar until fluffy. Beat in the egg and vanilla extract.
04 -
Alternately mix in the dry flour mixture and milk, blending just until combined.
05 -
Gently fold in the blueberries.
06 -
Spread the batter evenly into the prepared baking dish.
07 -
Mix sugar, cake flour, cinnamon, and cubed cold butter until crumbly. Sprinkle evenly over the batter.
08 -
Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean.
09 -
Allow the cake to cool for at least 10 minutes before serving warm or at room temperature.