Sift 5 ounces all-purpose flour, 1 Tablespoon dutch cocoa powder, 1 pinch ground cinnamon, and 1 ¾ ounces powdered sugar onto a work surface. Add 1 ounce ground walnuts, 3 ½ ounces unsalted butter (cold, cut into smaller pieces), and 1 egg yolk.
Begin working the dough. Start by using a fork to combine the wet and dry ingredients, then switch to your hands—I recommend wearing food-grade gloves. Be cautious: the mixture will initially be crumbly, and it might seem like it will never come together. However, be patient and keep kneading until a smooth dough forms.
Do not overknead. Once the dough holds together and is smooth, wrap it in cling film and refrigerate for a few hours, ideally overnight.
Roll out the rested dough on a lightly floured surface to a thickness of about 4 mm (a bit over ⅛ inch). Use a cookie cutter to make 1.½-inch (4 cm) diameter rounds and place them on a baking tray lined with parchment paper. Be sure to check the tips for working with this type of dough at the bottom of the recipe card.
For dough scraps, gather them into a ball, flatten into a disc, and refrigerate for a while to firm up. Once chilled, roll the dough out between a folded sheet of plastic wrap, turning it over several times to ensure even rolling. Cut out the rounds and transfer to a baking sheet.
Bake in a preheated oven at 350°F (180°C) for 8 minutes. Allow the cookies to cool completely on the baking sheet before handling.