Simply speaking, ganache is a mixture of chocolate and heavy cream. The addition of the cream to the chocolate changes the consistency that it will be at varying temperatures. Depending on the consistency of the finished ganache it has many uses, including filling cakes, making the centers of truffles, glazing pastries or it can be whipped into a mousse. Light gaanache is sometimes used a chocolate sauce.
Depending on the kind of chocolate used, and for what purpose the ganache is intended, the ratio of the chocolate to cream is varied to obtain the desired consistency. For truffles, the ratio is roughly 1 part cream to 3 parts chocolate, for filling cakes or making a base for a mousse, the ratio is roughly 1 part cream to 2 parts chocolate. For glazing pastries, the ratio is roughly 1 part cream to 1 part chocolate. These ratios are for using dark chocolate (approx 70 percent cocoa solids). As a general rule, as the percent of cocoa solids decreases, so should the amount of cream added relative to the amount of chocolate.
You should always use the best quality of chocolate available to you to ensure a smooth, richly flavored ganache. Here are the general steps for making a ganache at home:
1- Begin by measuring out the proper ratio of cream to chocolate. This should be done by weight, not by volume.
2- Chop the chocolate as small as possible, to facilitate even melting. One of the most efficient ways to do this is to use a sharp, serrated knife; the serration causes the chocolate to break into small shards as it is cut. Place the chocolate in a heatproof (preferably metal) bowl.
3- Heat the cream in a saucepan until almost boiling. You do not want to boil the cream or it will be too hot and the texture of the finished ganache will not be as fine. Also, you should avoid using a microwave to heat the cream, as it will not retain the heat as well as it would being heated over the stovetop.
4- Pour the cream over the chopped chocolate. Allow the mixture to stand, undisturbed, for a minute or two.
5- Stir the ganache gently until the cream is fully incorporated and the mixture is completely smooth. At this point, add any desired flavoring (flavored liqueurs, extracts, or purees). Depending on how you intend to use your ganache, it may be ready to use, or at this point be chilled.
Ganache should be intensely flavored, with the chocolate flavor enriched and smoothed by the addition of the cream. The texture should be smooth and dense. The more chocolate in the ganache the thicker it will be. When ganache is warm is should be very glossy and when cooled and whipped it becomes more opaque and matte.