I had some lime sugar cookies when I was at Fenway the last time. I wanted to try them for myself, so I took the Betty Crocker sugar cookie recipe and added the juice from one lime. The result: I can't really tell there's any lime in there. So, next time, I'm going for 2 limes, possibly with a little lime zest.
It would also be nice if I could get the cookies soft and chewy like the ones I had at Fenway. Unfortunately, I'd probably have to add all sorts of chemicals to get them that way.