Chocolate ganache is simply made by mixing equal quantities of double (or heavy) cream and chopped chocolate. The cream should be heated to just below boiling point and poured over the chocolate while it is still warm. Allow the cream and chocolate to stand for a few minutes to give the chocolate time to melt. The more finely the chocolate is chopped, the easier it will melt. You could even grate the chocolate on the largest holes of a cheese grater. For fail-proof results (ie chocolate that melts easily without turning into hard lumps in the cream) I would recommend using baking chocolate which is found in the baking aisle of the supermarket. I have also used an eating chocolate such as Cadbury's Dairy Milk. However, that said, I've had great results from using eating chocolate. Just ensure you use double cream rather than single cream. Also, be careful not to get the slightest drop of water near the chocolate, or you will end up with a hard mess that will have to be thrown away.