Preheat oven to 350 degrees F. Cream shortening with sugar and beat in the egg. Sift flour, baking powder, and salt together. Add dry ingredients to shortening-sugar mixture alternately with milk. Sprinkle washed, drained blueberries with a little flour to keep them from sinking, and stir into batter. Pour batter into a greased and lightly floured 7x11-inch pan. Mix together ingredients for crumb topping until crumbly. Sprinkle batter with topping. Bake for about 40 minutes or until cake tests done.