I have some questions about these two.
What is the difference between cream use for ganache and the heavy whip cream?
What is the difference between ganache and mousse?
and how come you can cover a cake in ganache(chocolate +cream) and roll fondant over it? How come fondant is not ruined?
If I am correct , chocolate ganache is: chocolate +cream(i am using whip cream), boiled and cooled.
cholocate Mousse is: eggs, chocolate+ cream, same whip cream. Boiled them, cooled and whipped.
Whipping cream has more fat than regular cream. If made correctly ganache will harden enough to cover with fondant creating nice shape edges. I did this for my cousins wedding cake last summer and it worked well. I use 12 ounces of semi sweet chocolate, 3/4 cup cream, 2 tablespoons butter and a splash of vanilla. Let cool at room temp over night before frosting your cake. You want to make sure you you use a hot knife so the ganache is nice and smooth because it will harden. You can also whip the ganache to create a filling using a mixer. I personally prefer a chocolate mousse made with two cups whipping cream and one small box of chocolate fudge instant pudding.
Sorry I forgot to add I think ganache is to sweet for my taste but others really like it.
The basic difference between ganache and mousse is indeed that mousse has eggs in it.
Both can be made with various types of cream (I've made sour cream ganache and it is yummy!), though plain old heavy (whipping) cream is most common, and with various types of chocolate, though ganache is most often done with a very dark, bittersweet chocolate while mousse is often lighter.
I'm not sure why you would think that putting fondant over ganache would ruin the fondant? Ganache can be poured while warm and then will harden as it cools, or it can be left to set in the bowl and then whipped to a creamy, spreadable consistency that is used the same way as any other frosting. But either way if you're using it under fondant you let it cool and harden first.