Substituting margarine for butter in a food as delicate as buttercream icing is not as straightforward as you might think. The chemistry of margarine is different from that of butter, which is one reason this is not a simple one-to-one substitution. If you are substituting for health reasons, keep in mind that neither butter nor margarine is particularly good for your health, so you should select a margarine with liquid vegetable oil or water as the first ingredient. This keeps the saturated and trans-fatty acids to a minimum.
Using an electric mixer, blend together the margarine and shortening.
Add the soy milk and vanilla to the creamed margarine mixture and combine well.
Stirring or mixing constantly, add the icing sugar slowly. Make sure there are no lumps and continue adding until the desired taste and consistency is achieved.
Add the Golden syrup and blend the entire mixture thoroughly.
This recipe makes about two cups of icing, and can be kept for up to two weeks.
This buttercream can melt or get soft quickly. Store it in the fridge until ready to use, especially if you plan to decorate using pastry bags.
The syrup in this recipe helps keep the frosting from cracking, but it is not essential.
Add 1 tsp of a flavoured extract or alcohol to create different versions, such as orange or rum buttercream.