A lot of ganache that I see for cakes, especially sculpted cakes or ones being covered in fondant, is not meant to be whipped. Those recipes use a higher proportion of chocolate so that, even if unwhipped and at room temperature, the ganache is solid. (In fact, sometimes the ganache needs to be warmed slightly to make it workable).
This particular recipe is for a whipped ganache, meaning that it is a little liquid even after it has been fully cooled. It uses less chocolate and has a much lighter taste and texture. It has to be whipped lightly to stiffen it, but particular care should be given not to over-whip it! Ganache curdles very easily. I always prefer to whip ganache by hand for this reason. As soon as it starts lightening in colour, I stop after every whip to check if it has started to curdle. The surface should look perfectly smooth.
If it starts to curdle, you've gone too far! Stop whipping right away. Add some unwhipped ganache into the overwhipped mixture and gently stir until incorporated. Sometimes this can help - sometimes not. Either way, it will generally taste the same, although the mouthfeel may be discernibly less smooth.
Recipe found after the break:
