I've read sooo many posts on freezing cakes filled or not to fill prior to freezing. What I need to know is: I've already frozen the cakes unfilled. Can I fill the cake as soon as I take it out of the freezer? Do I really have to wait for it to thaw first? Can I ice it while it's still frozen, as this is easier then when it is thawed? I'm just filling with buttercream.