1) Preheat your oven to 350°F. Lightly grease a baking sheet.
2) Stir butter into half of the cookie mix. Beat until well blended. Add the egg white and beat until fluffy.
3) Blend in the remaining cookie mix and nut flour. Be sure to scrape the bottom and sides of the bowl.
4) Shape into 4 flattened disks, wrap each in plastic wrap, and chill for 1 hour or overnight.
5) Dust your rolling surface with nut flour or cornstarch and roll one disk at a time until 1/4" thick. Cut out cookies. Transfer carefully to baking sheet. Dough can be re-rolled 2 or 3 times; chill between rollings for best results.
6) Bake the cookies for 9 to 12 minutes, till they're golden brown on the edges. Cool completely before decorating.
Yield: 2 to 3 dozen cookies, depending on size.