Preheat oven to 325 degrees F. Line an 11 by 16-inch baking sheet with parchment paper or use a silicone baking mat.
4 ounces of the chocolate chunks with the butter. Set aside the mixture to cool slightly.
In a medium bowl, sift
together the flour, baking soda
and cocoa. Whisk
in the espresso
powder and salt.
In the bowl of an electric mixer
, combine the chocolate mixture, sugars, egg
and vanilla at medium speed. Reduce the speed to low and add the flour in thirds. Turn off the mixer and fold in the remaining 4 ounces chocolate chunks.
Using a spoon or an ice cream scoop
, form the dough
into 1-inch balls and place on the prepared baking sheet, spacing 2 inches apart. Bake for 10 to 12 minutes or until the cookies have spread into disks and the tops are crackled. They will still be soft. Set the baking sheet on a cooling rack
and let the cookies
cool for about 2 minutes. Remove with a spatula
to a cooling rack to let cool completely.