Combine the chocolate and butter in a saucepan or in a microwave-safe bowl. Melt over low heat (on the stovetop) or on 50% power in the microwave at 1-minute increments, stirring in between, until smooth and melted. Let cool to room temperature.
In another medium bowl, whisk together the gluten-free flour, cocoa powder, salt, baking powder and baking soda. Set aside.
In a large bowl, whisk together the brown sugar, granulated sugar, eggs, espresso powder and vanilla until smooth. Whisk in the cooled chocolate/butter mixture. Stir in the dry ingredients.
Scoop and roll the dough into 1.5 tablespoon-sized balls (I use a #40 cookie scoop).
Roll each dough ball in granulated sugar, then roll generously in the confectioners’ sugar. Place on a small baking sheet or flat plate (that can fit in your freezer.)
Freeze the dough balls for 30 minutes, or up to overnight.
When you're ready to bake the cookies, preheat the oven to 325F. Line two large, rimmed baking sheets with parchment paper or silicone liners.
Place the frozen dough balls evenly on the baking sheet, about 3 inches apart. Bake for 11-13 minutes, until the edges are set and the center is mostly set. Cool the cookies for 3-4 minutes on the pan, then transfer to a wire rack to cool completely. Enjoy!