Instructions

Position oven racks in the upper-middle and lower-middle of the oven and preheat to 350 degrees. Line two large baking sheets with parchment paper.
In medium bowl, whisk together 2 cups (280 grams) all-purpose flour, ⅓ cup (30 grams) Dutch-processed cocoa powder, 1 teaspoon baking powder, and ¾ teaspoon fine sea salt.
In large bowl, using hand mixer, beat 1¼ cups (250 grams) granulated sugar and 2 sticks (8 ounces/225 grams) softened unsalted butter on medium speed until pale and fluffy, 2 to 3 minutes. Add 1 egg and beat until smooth. Beat in 1 tablespoon vanilla sugar. Add dry ingredients and mix on low speed until dough forms and no patches of dry flour remain. Cover bowl with plastic wrap and refrigerate for at least 2 hours or up to 1 day.
Divide dough into 4 equal portions and shape each piece into 12-inch-long log. Place 2 logs lengthwise on each baking sheet spaced 4 inches apart and flatten slightly with your hand. Brush logs lightly with 1 egg yolk beaten with 1 tablespoon water and sprinkle liberally with Swedish pearl sugar.
Bake until cookie logs are flattened and dry to the touch on top, 16 to18 minutes, switching racks and rotating baking sheets halfway through baking.
Transfer baking sheets to wire racks and let cookies rest for 10 minutes. While still warm, slide cookie logs on parchment paper onto cutting board and cut at slight diagonal every 1¼ inches to make slices. Transfer slices directly to rack to cool completely. Serve.