After you carve a frozen cake--what next? do you let it sit out to come to room temp? or cover it with plastic wrap and let it come to room temp? or buttercream and fondant it as is? thanks

After carving you need to crumbcoat it so it doesn't dry out (fill before carving). Then let settle for at least two hours to come up to room temp and then fondant. HTH

I let me sit for about 20 minutes before carving and then cover in ganache and then in fondant - depending on what I am carving out, sometimes it can take a while. I don't cover if still fully frozing but I have covered them partly frozen.

Good luck