Anything chow-worthy by Edinburgh airport?
The Airport Express takes about 20-30minutes to get into the centre of town (£6 return). Don't know what I would recommend, especially as I don't know what you mean by 'long layover'.
I've always wanted to try the seafood bar. There's also massage available. And you can sample whisky at the Duty Free.
I'm not sure what's available close to the airport, but BAA offers a Paul restaurant (French patisserie/bakery/sandwich spot) and also a seafood bar. There are other chains, too, like E.A.T. If it's a long layover, you're probably best getting into Edinburgh for a decent meal and look-see.