Hi!  I am new to cake decorating so please forgive me if this is a silly question.  I am making a Lego block cake for my nephew's birthday.  I'm baking a cake in a 13x9 pan then cutting it evenly into 3 lego blocks.  I want to get the corners and edges sharp so I'm reading that ganache is best to do that.  After I ganache, I'll let it set and the next day I am covering it in marshmallow fondant.  Do I need a thin layer of frosting on top of the ganache for the fondant to stick or will the fondant stick to the ganache?  Thank you in advance!

I've never iced a cake in ganache and covered it with fondant, but from tutorials I've watched, if you just lightly brush on some water before rolling out your fondant, it will get sticky and by the time you are ready to put the fondant on, it will stick to it just fine.

Thanks so much!!

I just give it a spray with some cooled boiled water or brandy. 

I just use a very light coat of vegetable shortening, or you can use a 50/50 mix of corn syrup and water and brush it or spray it on. It sticks really well with the shortening though. And if you mess up and need to pull the fondant off, it comes off very easily without messing up the ganache. 

AThanks very much everyone!