Chocolate ganache has to be one of my favourite fillings for cakes and desserts. It's simple to make and the proportions can be adjusted to suit the that it's accompanying.
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:
Whipped Dark Chocolate Ganache
Bring 1 litre heavy (whipping, 35%) cream to a boil. (Or heat until bubbles form at edge). Remove from heat.
Add in 400g-500g* dark chocolate pieces. Stir until all chocolate is melted and fully incorporated.
Allow to cool, and then refrigerate until fully chilled.
When ready to use, lightly whip the ganache until it has just started to stiffen. The colour should noticeably lighten.
*Why is there a range in weight? Depending on the amount of cocoa solids in the chocolate, more or less chocolate would be needed. More chocolate will be needed if it only has 50% cocoa solids compared to when using one which has 70%.