Heat the oven to 350 degrees. Cream the shortening, sugar, and egg substitute together. In a small bowl, make a thick paste of the cocoa and food coloring and add it to the cream mixture. Stir in the vanilla.
Sift together the flour, salt, and baking soda. Alternately add portions of the flour mixture and the buttermilk to the creamed mixture, stirring well.
Mix in the vinegar and pour the batter into a 2 x 9- by 9-inch or oblong pan. Bake for 30 minutes.
Allow to cool. Cut into 10 squares and top each square with whipped topping.