• Melt 4 tablespoons of butter in medium saucepan over medium heat.
• Add cocoa powder and espresso powder; stir until mixture forms smooth paste. Set aside to cool 15 - 20 minutes.
• In bowl of stand mixer fitted with paddle attachment, mix remaining 16 tablespoons butter, sugar, salt and cooled cocoa mixture on high speed until well combined and fluffy, about 1 minute.
• Add yolks and vanilla and mix on medium speed until combined.
• With mixer running on low, add flour in 3 additions, waiting until each addition is incorporated before adding next. Continue to mix until dough forms cohesive ball.
• Turn dough onto work surface; divide into three 4-inch disks.
• Wrap each disk in plastic wrap and refrigerate until dough is firm, yet malleable, 60 minutes.
• Line large baking sheet with parchment paper.
• Adjust oven rack to middle position and heat oven to 375°F.
• Roll out 1 dough disk between 2 large sheets of parchment paper to even thickness of 3/16 inch. Peel parchment from one side of dough and cut into desired shapes using cookie cutters.
• Place on prepared baking sheet, spacing them about 1 inch apart.
• Bake until cookies offer slight resistance to touch, 10 - 12 minutes.
• Cool for 5 minutes, then using spatula, transfer cookies to wire rack and cool completely.

Bittersweet Chocolate Glaze

• Melt 4 ounces bittersweet chocolate with 4 tablespoons unsalted butter and whisk until smooth.
• Add 2 tablespoons corn syrup and 1 teaspoon vanilla extract and mix until smooth and shiny.
• Use back of spoon to spread scant teaspoon glaze to edge of cookie.
• Allow glazed cookies to dry at least 20 minutes.