In a medium bowl, combine 2 cups of all purpose flour, 2/3 cup of unsweetened cocoa powder, 1 cup of cornstarch, 1 teaspoon of espresso powder, 1 teaspoon of baking powder and 1/2 teaspoon of salt and set aside for now
In a separate bowl, beat together 14 tablespoons of room temperature butter with 2/3 cup of granulated sugar until fluffy
Add 3 large egg yolks, 2 tablespoons of whole milk and 2 teaspoons of vanilla extract in with the butter and eggs and mix to combine
Gradually add the flour mixture and mix until just combined (do not overmix)
Form the dough into a disk and wrap tightly with plastic wrap
Chill the wrapped dough for about an hour or until firm
Unwrap the dough and cut the disk in half
Place one half of the dough between two sheets of parchment or wax paper and roll the dough to 1/4" - 1/8 inch thickness
Remove the top layer of parchment or wax paper and use a round cookie cutter to cut out the cookies
Transfer the cut out cookies onto parchment lined baking sheets
Transfer the baking sheets into the freezer for 15 minutes
Repeat the process with the second half of the dough while the first half chills
Preheat your oven to 350 degrees
Bake the cookies for 8 minutes
Transfer the baking cookies onto a cooling rack to cool fully before filling