- 1 1/4 cups (2 1/2 sticks) unsalted butter, softened
- 1 1/2 cups sugar
- 2 large eggs, plus one large egg white
- 1 teaspoon salt
- 1 tablespoon pure vanilla extract
- 1/2 cup milk
- 4 cups all-purpose flour, plus more for dusting
- 1 cup unsweetened cocoa powder
- Almond Dough
With an electric mixer on medium-high speed, cream butter and sugar until pale and fluffy. Beat in whole eggs and salt. Add vanilla, milk, flour, and cocoa; mix until incorporated.
Turn out dough onto a piece of plastic wrap, and shape into a rectangle; wrap. Chill until firm, at least 1 hour, or up to 1 day.
On a generously floured 12-by-26-inch sheet of parchment paper, roll out chocolate dough to an 11-by-24-inch rectangle, dusting with flour as needed and occasionally lifting dough with an offset spatula to prevent sticking. Chill again.
On another generously floured piece of parchment, roll out almond dough to a 9 1/2-by-24-inch rectangle, as described above.
Lightly beat egg white; brush over chocolate dough. Gently stack almond dough on top, aligning flush on one long side (there will be a 1 1/2-inch space on the other long side). Cut stack crosswise into thirds to make three 8-by-11-inch rectangles. Starting with the short side where the edges are flush, roll doughs together into a log, gently lifting parchment as you go. Lightly brush edge with egg white; seal seam by pinching and pressing gently. Wrap log in parchment or waxed paper. Repeat with remaining two stacked rectangles. Chill in freezer until firm, about 1 1/2 hours, or up to 1 month.
Preheat oven to 350 degrees. Line baking sheets with parchment paper. Let dough stand at room temperature 10 minutes. Using a serrated knife, cut log into 1/4-inch-thick rounds, rotating log after each cut to keep it round. Transfer rounds to sheets. Bake until set but not taking on any color, 18 to 20 minutes. Transfer cookies (still on parchment) to wire racks to cool completely. Cookies can be stored up to 5 days at room temperature in airtight containers.