I decided to look on the back of the packets of shop bought cakes that had 'buttercream', and they predictably contained no butter in the icing: in pretty much every case, it was palm oil, or hydrogenated vegetable fat. So, I took to the internet to see if people make icing with these fairly gross ingredients.
I did a search for 'buttercream with vegetable fat' or something like that, and I was brought to the official Wilton recipe for buttercream icing: it used butter and vegetable shortening in equal quantities, and lots of vanilla essence. At first, I was skeptical, not only because vegetable fat on its own is fairly disgusting, but because the vegetable fat that was being used in the video didn't resemble anything we have here in Ireland.
In the States, it seems, vegetable fat -- or shortening -- is soft and spreadable and bright white; it beats up like butter. Here, we get blocks of hard vegetable lard; it's made of the same stuff, only in a solid brick of a thing. I had utterly convinced it wouldn't whip or be beaten well like the American style stuff.
However, I got some just to try. I softened the butter and the fat to room temperature and used them both to make some vanilla buttercream icing. And, in complete honesty, I was thoroughly impressed.
- It is very stable: it's not prone to curdling or splitting like traditional buttercream made with only butter. It also holds its shape very, very well, which makes it perfect for piping
- The combination of vegetable fat and butter is quite bland: it doesn't have as strong a buttery taste, which makes it easier to flavour. You don't need as much essence, powder, or what-have-you.
- It's cheaper: a pound of butter is about €2.40, whereas a pound of vegetable fat is half the price at €1.20. So, if you mix them in equal quantities, you save 60c per pound.
- It whips up really quickly: the vegetable fat catches more air bubbles and makes something akin to whipped cream icing, but it doesn't go off like cream does. It'd make a nice filling for fondant fancies or the like.
- It's pale, therefore easy to dye.
- The butter and fat take a lot of beating to come together. You need to work them a lot with a wooden spoon and a strong wrist, or with an electric beater. HOWEVER, if going the electric option, use it to mix the butter and fat only until beaten, otherwise....
- It whips up really quickly: if you use an electric beater to mix in the icing sugar, you will end up with something that's more like whipped cream than buttercream. So when adding the icing sugar, switch to a wooden spoon.
- It's a little more greasy in mouthfeel than traditional all butter icing, and doesn't have the smoothness of butter.
- It's fairly bland if you don't add enough flavouring, because it lacks the richness of the butter. You might want to add a baseline of vanilla essence in underneath whatever flavour you're adding in.
Long story short: Make sure the butter and fat are well and tempered to room temperature. Mix the butter and fat together really well on their own first. Don't over mix once you add the icing sugar. Add vanilla essence no matter what flavour you're making it for more depth. Forgive it its slightly greasy mouthfeel.