I have always used a frosting like buttercream under my fondant.
I am now going to frost with a rather firm ganache instead.
Does the fondant adhere to the ganache, or do I have to soften it a bit first so it has some grab to it??
You can brush your ganache very lightly with sugar syrup. You do not want to soften your ganache on the cake or you will end up with dents instead of a nice smooth surface.
I spritz mine very lightly with water, or lightly rub with a damp paper towel. It works fine.