Preheat oven to 350 degrees. Put sifted flour, sugar, cocoa in 8 inch square pa n. Add salt and baking soda and mix well. Now make 3 holes in flour mixture in pan spaced out evenly across the top. Put vinegar in first hole, water and v anilla in second hole and shortening in third hole. Mix well until smooth. Ba ke for 35 minutes. Frost with fudge frosting