I've dealt with this twice. Once, I had to dump the batch. I bottled and it was still nasty a month later. Dumpola. Maybe it would have recovered, but I'm not getting any younger so I'm not waiting.
Second time was a barleywine. I think it has finally, after 2 years, lost most of that green apple.
What I would do if I had this happen again is grow a big yeast starter, then add it to the beer, along with a pound of DME. Acetaldehyde is an intermediate alcohol that should get cleaned up by the yeast. No idea why this doesn't happen sometimes, but I'm throwing more good yeast at it next time.
Revvy might be right, don't want to argue there, but in my experience bottle conditioning didn't help (much).