To make streusel, combine dry ingredients in bowl.
Cut butter into dry ingredients with pastry blender or forks until crumbly. Set aside.
Grease 8x8" glass baking dish
Preheat oven to 375.
Whisk together flour, baking powder and salt.
In a large bowl, cream sugar butter and egg until well blended.
Gradually add dry ingredients and milk to this bowl, beating constantly.
Fold blueberries into batter just until distributed.
Pour/spread batter into prepared disk.
Spread topping evenly over batter.
Bake for 45-50 minutes, until toothpick inserted in center comes out clean.
Allow to cool completely before cutting and serving.