Cake: Cream together sugar and butter, add eggs and beat. Combine flour , baking powder and salt. Add to creamed sugar mixture alternately with milk. Mix for 2 mins. Fold in blueberries. Pour batter into greased and floured 9x13" cake pan.
Crumb topping:
Add sugar, flour and cinnamon and combine. Slice cold butter and add. Take two knives or a pastry cutter and cut until mixture becomes crumbly. Sprinkle crumb topping evenly over batter.