The Flavor Thesaurus by Niki Segnit.
My recent post Iced Lemon Butter Cookies

These look delightful. :) I love that you added cornstarch - I subbed potato starch for part of the flour in a batch I made last week and they're so crumbly-crisp and not hockey-puck-hard. Didn't think to add colored sugar afterwards instead of regular sugar. Very festive!