I'm also torn between Mayo and Mado for the reasons outlined here, which is why I've searched Google for the clue and ended up at this page!
I'd be more inclined towards Mado, except that according to this site -
http://www.seafriends.org.nz/enviro/fish/kypho /kyphosid.htm#mado - "Mado is not normally fished. It does not occur in sufficient numbers and won't take bait easily", which doesn't suggest that it is actually eaten. I have found no evidence that it is ever eaten anywhere. So it therefore surely doesn't qualify as 'food', does it?
But I'm equally sceptical about Mayo, because (a) there is no word for 'made' that is mostly 'may', and (b) I don't think it's true that 'MAde' with 'YOlk' is *mostly* 'MAYO' - it's only half of it. And that's without getting into whether 'egg' really suffices to indicate 'yolk', which is surely only a part of an egg.
So while I want the answer to be mayo because then it would mean the whole clue was a great definition, I really can't get the cryptic bit to work for this; and I'm just not convinced about mado either.
The full list of food items I have found that fit this space is:
Mayo
Sago
Lalo (another word for couscous, apparently)
Taco
Taro (an edible tuber, apparently)
and of course the not-actually-food Mado.
Can anyone see how it could be any of the others, or am I going to have to take a stab in the dark and go with Mayo (or Mado, or one of the others, at random)?
It's so frustrating, after I was so delighted to have at last fought my way through the rest of this complicated crossword!