Instructions

• In a large bowl, beat the softened butter and granulated sugar with a hand mixer or stand mixer fitted with the paddle attachment until light and fluffy, about 1–2 minutes. Scrape down the bowl as needed.
• Add the egg yolk, baking powder, salt, and vanilla extract. Mix on low speed until combined and smooth.
• Add the all-purpose flour and mix on low speed just until a soft dough forms and there are no large streaks of flour. Do not overmix.
• Divide the dough into two equal portions. Shape each portion into a log about 6–7 inches long and approximately 1½ inches in diameter, smoothing seams so each log is uniformly cylindrical.
• If using sanding sugar: pour a layer of sanding sugar onto a large flat surface (a sheet of parchment or a baking sheet works). Roll each log in the sanding sugar, pressing gently so the sugar adheres evenly. If not using sanding sugar, skip this step.
• Wrap each log tightly in plastic wrap. Stand the wrapped logs upright in glasses if needed to keep them circular. Chill the logs in the refrigerator for at least 2 hours or up to overnight until firm.
• When ready to bake, preheat the oven to 350°F. Line cookie sheets with parchment paper or silicone baking mats.
• Unwrap a chilled log and, using a sharp knife, slice the log into rounds no more than 1/4 inch thick. Place the slices on the prepared cookie sheets, spacing them about 1 inch apart.
• Bake the cookies in the preheated oven for 16–18 minutes, or until the edges turn light golden and the tops are no longer glossy. Rotate the pans partway through baking if your oven heats unevenly.
• Let the cookies cool on the baking sheets for 5–10 minutes, then transfer them to a wire rack to cool completely.
• Store cooled cookies in an airtight container at room temperature for up to 5 days, or freeze for up to 3 months.