Stir together flour, cocoa, espresso, baking powder, and salt in a medium bowl.

Beat butter and brown sugar with a mixer until light and fluffy, about 3 minutes.

Beat in egg until well combined; mix in cooled Bittersweet Chocolate.

Reduce speed to low, and gradually add flour mixture; beat in milk until just combined. Cover dough with plastic wrap.

Freeze until firm, about 45 minutes.

Preheat oven to 350°F.

Line 2 baking sheets with parchment.

Shape dough into ½-inch balls (exactly 1 teaspoon each).

Pour confectioners' sugar into a medium bowl; working in batches, roll balls in sugar 2 times, letting them sit in sugar between coatings.

Put onto cookie sheet 2 inches apart.

Bake until cookies have spread and coating has cracked, 10 - 12 minutes