BLACK-AND-WHITE-AND-GREEN COOKIES

Steps:

• Whisk baking powder, 2½ cups flour, and 1½ tsp. salt in a medium bowl to combine. Pulse mint and granulated sugar in a food processor until mint is finely chopped. Add butter; process to combine. Add dry ingredients and pulse again to combine. Add egg and egg yolk; pulse until a shaggy dough forms.
• Turn out dough onto a lightly floured surface and knead just until dough holds its shape. Divide dough in half; pat each portion into a 1"-thick disk. Wrap disks in plastic and chill until firm, at least 2 hours.
• Place racks in upper and lower thirds of oven; preheat to 350°F. Working with 1 disk at a time, roll out dough on a lightly floured sheet of parchment paper to about ¼" thick, dusting with more flour as needed to keep from sticking. Punch out rounds with lightly floured cookie cutter and arrange on 2 parchment-lined baking sheets, spacing 1" apart. Pat dough scraps into a 1"-thick disk. Wrap in plastic and chill 10 minutes if soft. Repeat process with scraps.
• Hold a bench scraper or straightedge upright 1" from edge of a cookie to cordon off a shallow semicircle (do not press down into dough; you're just making a barrier). Coat semicircle with sanding sugar; gently press to adhere. Remove scraper; you should have a tidy sugared edge. Repeat with remaining cookies and more sanding sugar.
• Bake cookies, rotating baking sheets top to bottom and back to front halfway through, until edges are lightly browned, 10-12 minutes. Let cool 10 minutes on baking sheets, then transfer to 2 wire racks set inside 2 rimmed baking sheets; let cool completely.
• Sift powdered sugar and cocoa powder into a medium bowl. Add corn syrup, a pinch of salt, and 2 Tbsp. warm water and stir until smooth and glossy.
• Position bench scraper to make another shallow semicircle on the other side of the cookie, angling it so that it forms a V with the sugared edge, lightly pressing scraper into cookie to make a barrier. Spoon 1 tsp. glaze onto exposed semicircle and use a toothpick to help coat evenly; excess will drip over sides. Lift scraper straight up and over chocolate side to create a neat edge. Repeat with remaining cookies and glaze. Let sit until glaze is set, at least 2 hours.
• Do Ahead: Dough can be made 1 month ahead; freeze. Thaw in refrigerator before using. Cookies can be baked 1 day ahead; store tightly wrapped on a rimmed baking sheet at room temperature.