A question about a recipe: Chewiest Sugar Cookies

I would use food-grade lemon essential oil. A few drops should be more than enough.

i agree and would say that you could also substitute a little lemon extract/ lemon juice for the vanilla. just make sure to not overdo it when using extract. putting a nice lemon glaze over them would also be very tasty too

You could probably just add a little (or a lot!) of lemon zest for a nice lemony zing! I've done that many times with shortbread cookies, scones, etc. and I would bet that it would work just fine with these as well!