-
Preheat oven to 375°F and grease a 9×9 baking dish.
-
In a bowl, whisk the flour, baking powder, and salt.
-
In another bowl, beat the butter and sugar until fluffy. Beat in the egg and vanilla.
-
Alternately mix in the flour mixture and milk, blending just until combined.
-
Fold in the blueberries gently.
-
Spread the batter evenly into the prepared pan.
-
Make the streusel by mixing the sugar, flour, cinnamon, and cubed butter until crumbly. Sprinkle over the batter.
-
Bake for 35-40 minutes until a toothpick inserted in the center comes out clean.
-
Allow to cool at least 10 minutes before serving warm or at room temperature.
