I'd never used ganache before, though I'd heard people talk about how wonderful it is. On my favorite cake forum, Cakecentral.com, I'd read posts where people said that they now use ganache under all of their fondant cakes instead of buttercream because it is so much easier to work with. Trying something new I'd never even tasted, though, was a bit scary, until I looked at a recipe, look how simple it is!
3 lbs finely chopped, semi-sweet chocolate
3-1/2 C heavy whipping cream
Slowly bring the whipping cream to a boil, then pour into a bowl containing your chocolate and stir until smooth. The cake needs to chill for a couple of hours after you put the ganache on it so it can set up nice and hard before you start putting on fondant. A warm spatula will help smooth out the rough edges. If you like a thicker ganache, use more chocolate, if you like yours thinner, use less. This makes enough for 2-8" round double-layer cakes, but it keeps for a couple of weeks in the fridge, so if you have another cake coming up, put it in an air-tight container and refrigerate. It will stay good on the counter in an air-tight container for 3 days.
I used semi-sweet chips, which worked beautifully on my chocolate cake but chips don't melt as well as finely chopped blocks of chocolate (because of size, not melt-ability), so be aware of that. I know my sister says she uses blocks of chocolate and usually uses at least half unsweetened. The beauty of this recipe is that you could use just about any flavor of chips you'd like, or use white chocolate and candy flavoring to complement the cake flavor.
When I used this ganache for the first time, I actually torted both of my 8" circles, so there was ganache between each 1" layer of cake--which is a lot, so you could easily skip the torting all together. Also, I had frozen my cakes before putting the ganache on them, which helped the ganache to solidify much quicker so I could layer a little extra where the sides weren't exactly straight. You'll want to get the surface as perfect as possible before refrigerating because fondant shows every little bump beneath the surface, and only so much fixing can be done with the warm spatula later.