Whisk together the flour, cocoa powder, espresso powder, baking powder, salt and baking soda in a small bowl.
Melt the chocolate and butter in a medium microwave-safe bowl in the microwave in 1-minute increments, stirring in between, until smooth. Let cool slightly.
Beat the brown sugar and eggs with an electric mixer on medium-high speed in a large bowl until thick, about 2 minutes. Scrape the chocolate mixture into the egg mixture and beat until incorporated. Add the flour mixture and beat until just combined. Refrigerate the dough until firm, at least 2 hours and up to overnight.
Position oven racks in the top and bottom thirds of the oven and preheat to 350 degrees F. Line 2 baking sheets with parchment paper.
Put the confectioners' sugar in a small bowl. Scoop out tablespoonfuls of the dough and roll them into balls. Refrigerate half the dough balls. Toss the remaining balls in the sugar, coating them very generously (you shouldn't see any dough peeking through). Arrange the balls about 1 inch apart on the prepared baking sheets.
Bake until the cookies spread, the tops are dull in color and cracked and the edges are firm, 12 to 14 minutes. Let cool on the baking sheets for a few minutes, then transfer to a wire rack to cool completely. When the baking sheets are cool, repeat with the remaining dough balls. The cookies can be stored in an airtight container at room temperature for up to 3 days.
When measuring flour, we spoon it into a dry measuring cup and level off the excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)
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