How to Make It
Using paddle attachment, beat butter and sugar in a medium bowl with a mixer on medium speed until smooth. Beat in egg yolk and vanilla. Add 1 1/4 cups flour and beat until well blended. Using end of a tooth-
pick, add 2 small smears of green food coloring and 1 of black and blend well. Add more coloring as needed until dough is dark green. Flatten dough into a 1-in.-thick disk. Wrap in plastic wrap and chill about 30 minutes (or longer if it’s still sticky).
Preheat oven to 300°. On a floured board, roll dough 1/8 in. thick. Cut out leaves with a 3 1/2- to 4-in. by 2-in. oak leaf cookie cutter*. Set leaves on 2 ungreased baking sheets, then reroll scraps as needed. With edge of a small metal spatula or a toothpick, score leaves to make veins.
Bake cookies until slightly darker at -edges, 15 to 20 minutes, switching pan positions halfway through. Let cookies cool on baking sheets a few minutes, then transfer to racks to cool completely.
*Find Wilton gel paste food coloring at -Michaels stores and on amazon.com. Find Foose oak leaf cookie cutter on amazon.com.
Make ahead Up to 2 days, airtight at room temperature, or up to 1 month, frozen.