Mix sugar, flour and shortening until lumpy. Do not mix until creamy. Take out 1 cup for topping. Dissolve soda in hot coffee and add to the flour mixture. Also add egg and vanilla. Spread on sheet pan 9x12x2 inch and sprinkle on topping. This is a thin batter. Bake at 325-350ºF. approximately 30 minutes. Sprinkle with powdered sugar after baked.