¼teaspooninstant coffee or espresso powder, optional
Instructions
In a medium bowl, whisk together flour, baking powder and salt. Set aside.
In the bowl of a stand mixer (or using a hand mixer), beat butter and 1 cup sugar together on medium speed until light and fluffy, about 3 minutes. Scrape down the sides and bottom of the bowl halfway through. Add egg, egg yolk and vanilla. Mix until combined, about 30 seconds.
With the mixer on low, slowly add the flour mixture to the bowl. Mix just until combined. Batter will be thick. Use a spatula to scrape the bottoms of the bowl to ensure all flour bits are mixed in.
Divide the dough in half. It doesn’t have to be perfect. If one seems slightly smaller, use that for the chocolate dough.
Put one half back in the mixer. Add the cocoa powder, milk and instant coffee (if using). Mix until combined.
On a lightly floured surface, shape the vanilla dough into a 4x4 square. Wrap in plastic wrap and place in the refrigerator. Repeat with the chocolate dough. If the surface needs more flour, add more or use cocoa powder to dust the surface.
Chill the dough for 1 hour. Dough should still be malleable after chilling.
Place vanilla dough between two sheets of parchment paper. Use a heavy rolling pin to roll dough into a rectangle, about 7 inches by 14 inches. Pro tip: Place a silpat mat underneath to prevent parchment paper from sliding.
Repeat the process with the chocolate dough.
Remove the top piece of parchment paper from the vanilla dough. Remove one sheet of parchment paper from the chocolate dough as well. Very carefully place the chocolate dough on top of the vanilla dough. Press down gently so the two doughs press together, then peel away the parchment paper from the chocolate dough. Use your fingers to press together broken pieces. Use a sharp knife to straighten the edges.
Starting with the long edge of the rectangle, tightly roll the dough into a log. Peel away the bottom piece of parchment paper as you roll.
Wrap the log of dough in plastic wrap and refrigerate for at least 2 hours. Rotate the log after 30 minutes to make sure the bottom doesn’t get flat.
Preheat oven to 350 F. Line a baking sheet with parchment paper and set aside.
Sprinkle a work surface with ¼ cup sugar. Remove the log of dough from the refrigerator and discard the plastic wrap. Gently roll the dough over the sugar so the outside is coated. Use a sharp knife to cut the log into 1/2-inch thick discs. Place discs on the prepared baking sheet about 1 inch apart. If working in batches, keep remaining dough in the refrigerator.
Bake at 350 F for 14 minutes or until edges are set and golden. Cool on the pan for a few minutes before transferring to a wire rack to cool completely.
Notes
Store cookies in an airtight container at room temperature for up to 1 week.Freeze dough for up to 3 months. Wrap the dough log in a double layer of plastic wrap to avoid freezer burn. Store in the freezer, then defrost in the refrigerator before slicing and baking.