Step one, put the chocolate in a bowl. I used chocolate chips here, but you can use any good chocolate, chopped up or in chip form.
Step two, heat the cream . Take it off the heat before it boils.
Step three, pour the hot cream over the chocolate and let it sit for a couple of minutes to melt the chocolate.
Step four, whisk the chocolate and cream together until it smooths out and has a shiny appearance.
If using the mixture to cover a cake, let it cool to room temperature, then pour it over the the smoothly crumb-coated cake. To make the truffle filling, you should put the ganache in the fridge to cool off. When it's cool but not set, take it out of the fridge and whip it with an electric beater.
Step 5. Whip the cold ganache on high speed with an electric hand mixer or stand mixer. The color will lighten and the ganache will get fluffy and more solid.
This picture shows the difference in color between the whipped truffle and the unwhipped ganache on the edge of the bowl. Once the truffle has been whipped and is stiffer, but still spreadable, you can use it on cakes as a filling or frosting. After it's refrigerated for a while it should stiffen up and be more solid. When it's cold it should be too stiff to spread, though, so make sure that you use it on cakes before it's refrigerated, or you'll probably have to re-whip it before using it.
The ratios for different chocolates when making ganaches varies based on the type of chocolate and how stiff the end product needs to be. The more cream, the softer the resulting truffle will be. The basic ratio is about 1 part cream to 1 part chocolate or 1 cream to 2 chocolate for dark chocolates, and 1 cream to 3 chocolate for white chocolates. I use about 8 ounces cream to 12 ounces dark chocolate for most fillings.
Truffles and ganaches can be flavored using liquers, herbs, and other flavorings by either infusing the cream while it's heating up, or by adding the flavorings to the warm ganache.