Beat egg whites until stiff. Add ¼ cup sugar. Cream shortening; add salt and vanilla. Add ¾ cup sugar gradually. Add egg yolks; beat until light and creamy. Set aside a small amount of flour. Sift remaining flour and baking powder; add alternately with milk to egg yolk mixture. Fold in beaten egg whites. Dredge blueberries in remaining flour. Fold into batter. Turn into a greased 8-inch square pan. Sprinkle top of batter lightly with sugar. Bake at 350 degrees for 50 to 60 minutes.