I have to ice a cake from Monday and I baked the cake already and just froze it. can I take it out Sunday night, ice the cake and put it in the fridge for Monday? or shoudl I defrost it first and than ice it for better resolts?
Cake thaws in under an hour. It's not like hamburger that takes hours and hours.
If you ice a frozen cake, and use a crusting BC, the BC will take longer to crust because of the extra moisture caused by the frozen state of the cake.
So if you take it out of the freezer Sunday night and crumb coat it, just leave it on the counter over night and finish it monday as planned.
Just FYI: I have experienced buttercream cracking after putting it on a frozen cake. May not be true for all types of buttercream, but I have had it happen with shortening based buttercreams years ago.
It can also cause air bubbles/blowouts in the bc from the cake expanding while defrosting.