I am trying to do some of the recipes from Garrison book but I have a problem with the ganache. I make it with couverture, because I can't find chocolate in Greece, and the ganache is very soft. Even though I waited a day to dry. The only solution I found is to increase the amount of couverture that is said on the recipe (almost 250%), but in this way the result is a totally different thing. Any ideas what should I do?