Preheat oven to 350 degrees.
Cream butter and 3/4 cup sugar for 2 minutes with mixer on medium speed.
Add egg and beat another 2 minutes.
In a separate bowl, blend 2 cups flour, baking powder, and salt together.
Add half of the flour mixture to butter mixture.
Add milk and then the rest of flour mixture to butter mixture and mix on medium until blended together
Spread in a greased 11x7 pan and top with blueberries.
In a medium bowl mix together 1/2 cup sugar, 1/2 cup flour, cinnamon, and butter. Mix together until it becomes crumbly.
Sprinkle on top of berries.
Bake for 45 minutes.