I thought I would share my experience so that no one else would have to go through what I went through.
Well, I was planing on making a WASC cake with lemon buttercream filling, then crumb coat with a white chocolat ganache and cover with fondant. Just so happens my local store had Lindt chocolate bars on sale. I thought "great!" since they are expensive. I go there and they are sold out of white chocolate. I went to two other locations, same thing. I looked at other stores. No white chocolate. Then I saw a bag of Hershey's Bliss white chocolate. I saw cocoa butter as one of the ingredients and thought it would work. WRONG! I made the ganache the night before, 3:1 ratio. It turned out beautifully. I coated my cake and was falling in love with ganache (first time using ganache under fondant) I was chilling the cake ind the fridge and I noticed my leftover ganache stared to separate. I started to worry, but proceeded on. I covered the cake with fondant and was almost done applying my fondant decorations when I noticed the sides were drooping. I looked at the leftover ganache and it was worse. It looked like a layer of liquefied butter on top of soft white chocolate. If it was looking like that in the bowl, I wondered what it was doing under the fondant. Luckily I had more than enough BC and fondant. I scraped everything off and redid the cake with BC and fondant. It caused me to be a few hours behind schedule and stayed up till 2 in the morning working on the cake. In the end it worked out fine and the couple loved their cake! Lesson learned, do not use Hershey's Bliss chocolate for ganache.
If you get your cream too hot, it can cause issues for the chocolate and have it separate and get oily.
Hmmm... I did not know that. Thanks for that tip! Maybe I will give it another try.