I would like to make an icing for my family member who has a milk allergy. I have a recipe for whipped fluffy icing using whole milk, flour, sugar and margerine. It is cooked, then cooled and additional steps follow. Will it turn out well if I substitute soy milk and vegan margerine? Also, can it be refrigerated?
Yes. Soy milk (or any other non-dairy milk such as almond milk) can be used as a direct substitute for dairy milk. (Your mileage may vary if you make homemade soy milk, which may have a more "beany" flavor.) In addition, vegan margarine such as Earth Balance can be used as a direct substitute for butter. In fact, these are two of the easiest vegan substitutions.