The word ganache from France meaning glaze or icing
Ganache is simply a mixture of chocolate with cream proportion varies as per the need.
How to make: Roughly cut the chocolate put it in a bowl add warm cream over the chocolate. Mix and keep aside.
Proportion: one part cream with 1 part chocolate. It can be used to make glazing for a cake. Medium ganache one part cream with 2 part chocolate. Hard ganache one part cream with 3 part chocolate
Usage: ganache can be used as glazing for cake, for filling and Base for truffle..and to make some desserts as well as sauce.
Variation: dark chocolate ganache and white chocolate ganache.