Preheat oven to 375 degrees. Grease and flour a 9 x 9 baking pan or dish.
In a medium bowl, sift together flour, baking powder and salt. (Cake ingredients)
In mixing bowl of a stand mixer cream together sugar and butter until fluffy. Add in egg and mix again until combined.
Mix in 1/3 of the flour mix and 1/3 cup of milk until combined. Repeat with 1/3 of flour mix and 1/3 of milk, then repeat with remainder of flour and the milk. Batter should be a thick consistency.
Using a spatula fold in blueberries. Spread the mixture into the prepared baking dish evenly.
In a small bowl, blend together sugar, flour, cinnamon, and butter (topping ingredient list) until crumbly. (Use forks or a pastry blender.) Sprinkle over the batter in the pan.
Bake in preheated oven for 35-45 minutes until toothpick comes out clean from center of cake. This recipe can be served warm or cooled.