My customer want a hand painted scene of a lake on a buttercream sheet cake.Should I freeze or chill it before I paint on it? I do not have an airbrush.

Where I am, if I freeze or chill a cake I have to deal with condensation, so my answer for that would be no.

I've painted on a (crusting) buttercream cake using airbrush colors and an artist brush. You want a soft brush and a soft touch, but you can do it.

Another option would be to make a fondant or gumpaste plague and paint on that. Then they can remove the piece and save it.

For hand painting, I'd say--they have to go with fondant. Too much headache to deal with bc. Or do the plaque idea. Or an edible image if you have access to that. Or pipe a design in royal icing, then paint that.

Good luck!