Melt the chocolate in a water bath. Add the butter in small pieces, mix thoroughly and remove from the heat.
Roughly chop the nuts using a blender and add to the chocolate mixture together with the icing sugar, vanilla extract andcognac. Mix well and put in the fridge for 1 1/2 - 2 hours.
Take the mixture out of the fridge and make it into small balls. Roll each ball in cocoa, coconut, chocolate sprinkles, or whatever else you wish to decorate your truffles with.