Chocolate Butter Cookies

1. FOR THE COOKIES: Melt 4 tablespoons butter in medium saucepan over medium heat. Add cocoa and espresso; stir until mixture forms smooth paste. Set aside to cool, 15 to 20 minutes.
2. Using stand mixer fitted with paddle, mix remaining 16 tablespoons butter, sugar, salt, and cooled cocoa mixture on high speed until well combined and fluffy, about 1 minute, scraping down bowl once or twice with rubber spatula. Add egg yolks and vanilla and mix on medium speed until thoroughly combined, about 30 seconds. Scrape down bowl. With mixer running on low, add flour in 3 additions, waiting until each addition is incorporated before adding next and scraping down bowl after each addition. Continue to mix until dough forms cohesive ball, about 5 seconds. Turn dough onto counter; divide into three 4-inch disks. Wrap each disk in plastic wrap and refrigerate until dough is firm yet malleable, 45 minutes to 1 hour. (Alternatively, shape dough into log, about 12 inches long and 2 inches in diameter; use parchment paper to roll into neat cylinder and twist ends to seal. Chill until very firm and cold, at least 1 hour.)
3. Adjust oven rack to middle position and heat oven to 375 degrees. Line 2 baking sheets with parchment paper. Working with 1 piece of dough at a time, roll 3⁄16 inch thick between 2 large sheets parchment paper. If dough becomes soft and sticky, slide rolled dough on parchment onto baking sheet and refrigerate until firm, about 10 minutes.
4. Peel parchment from 1 side of dough and cut into desired shapes using cookie cutters; place shapes 1 inch apart on prepared baking sheets. (For cylinder-shaped dough, simply slice cookies 1⁄4 inch thick and place on prepared baking sheets.) Bake 1 sheet at a time until cookies show slight resistance to touch, 10 to 12 minutes, rotating baking sheet halfway through baking; if cookies begin to darken on edges, they have overbaked. (Dough scraps can be patted together, chilled, and rerolled once.) Let cookies cool on baking sheet for 5 minutes; transfer cookies to wire rack and let cool to room temperature. Decorate as desired.
5. FOR THE GLAZE (OPTIONAL): Melt bittersweet chocolate with butter in heatproof bowl set over saucepan of barely simmering water; whisk until smooth. Add corn syrup and vanilla extract and mix until smooth and shiny. Use back of spoon to spread scant 1 teaspoon glaze almost to edge of each cookie. (If necessary, reheat to prolong fluidity of glaze.) Allow glazed cookies to dry at least 20 minutes.

GLAZED CHOCOLATE-MINT COOKIES
Replace vanilla extract with 2 teaspoons mint extract. Glaze cookies with Bittersweet Chocolate Glaze and dry as directed. Melt 1 cup white chocolate chips and drizzle over glazed cookies. Let dry at least 20 minutes before serving.

MEXICAN CHOCOLATE BUTTER COOKIES
In medium skillet over medium heat, toast 1⁄2 cup sliced almonds, 1 teaspoon ground cinnamon, and 1⁄8 teaspoon cayenne until fragrant, about 3 minutes; set aside to cool. In food processor fitted with metal blade, process cooled mixture until very fine, about 15 seconds. Whisk nut-spice mixture into flour before adding flour to dough in step 2. Proceed with recipe, rolling dough into log. Roll chilled log in 1⁄2 cup raw or sanding sugar before slicing.