1) Cream together the margarine and the shortening. Add sugar and beat forat least 5 minutes. Add the vanilla then the soy milk 1 tablespoon at a timewhile continuing to beat. Depending on the weather and the humidity of you kitchen will decide how much liquid you add. Stop adding soymilk when you arehappy with the consistency but continue to beat for at least another 5 minutes you want a very fluffy, very creamy consistency.
If you are going to be doing a lot of decorating, like roses and other flowers,you may want to double the recipe.
I have used this exact recipe for years. Everyone always loves it.