Ingredients

• 1 cup pecans
• 1 cup buckwheat flour
• 3/4 teaspoons kosher salt
• 1/2 teaspoons baking powder
• 1 cup all-purpose flour, plus more for surface
• 1 cup (2 sticks) unsalted butter, room temperature
• 2/3 cup powdered sugar
• 2 teaspoons vanilla extract
• 2 teaspoons granulated sugar
• 1 teaspoon white sesame seeds (not toasted)
• 1 teaspoon black sesame seeds
• 1/2 teaspoons poppy seeds

Instructions

1. Preheat oven to 350°. Toast pecans on a rimmed baking sheet, tossing once or twice, until lightly browned and beginning to smell nutty, 5-8 minutes (do not toast them all the way; they will get baked again). Let cool. Turn off oven.
2. Pulse pecans, buckwheat flour, salt, baking powder, and 1 cup all-purpose flour in a food processor until pecans are finely ground.
3. Using an electric mixer on medium. high speed, beat butter, powdered sugar, and vanilla until light and fluffy, about 4 minutes. Reduce speed to low and mix in dry ingredients just to blend. Divide dough in half; wrap each in plastic wrap, flattening into 1/2"-thick disks. Chill until very firm, at least 2 hours.
4. Working with 1 piece at a time, roll disks of dough between 2 lightly floured sheets of parchment paper to about 1/8" thick. Transfer to a baking sheet and remove top sheet of parchment. Chill 30 minutes.
5. While dough is chilling, mix granulated sugar, sesame seeds, and poppy seeds in a small bowl. Reheat oven to 350°. Using a knife or pastry cutter, cut out 2" squares or diamonds from dough and space out on baking sheet, about 1/2" apart. Sprinkle with sesame mixture and bake cookies until golden brown around the edges, 10-12 minutes. Transfer cookies to wire racks and let cool before serving.
6. Do ahead: Dough can be made 5 days ahead; keep chilled. Cookies can be baked 2 days ahead; store airtight at room temperature.