1/2 cup all-purpose flour
1/4 cup unsweetened cocoa powder
4 tsp instant espresso powder
1 tsp baking powder
1/8 tsp salt
4 Tbsp unsalted butter, room temperature
2/3 cup packed light-brown sugar
1 large egg
4 ounces bittersweet or semisweet chocolate, melted and cooled
1 Tbsp milk
1/2 confectioners' sugar, for coating
1. In a medium bowl, whisk together flour, cocoa, espresso, baking powder and salt. With an electric mixer, beat butter and brown sugar until light and fluffy. Beat in egg until well combined; mix in cooled chocolate. With mixer on low speed, gradually add dry ingredients; beat in milk just until combined. Flatten dough into a disk; wrap in plastic. Freeze until firm, about 45 minutes.
2. Preheat oven to 350 degrees. Line two baking sheets with parchment paper. Shape dough into 1-inch balls. Place confectioners' sugar into a medium bowl; working in batches, roll balls in sugar twice.
3. Place balls on prepared baking sheets, 2 inches apart. Bake, rotating sheets halfway through, until cookies have spread and coating is cracked, 12 to 14 minutes; cookies will still be soft to the touch. Transfer to wire rack to cool completely.