Preheat oven to 325°F. Line 2 baking sheets with parchment paper or a silicone baking mat. Set aside.
In a medium bowl, whisk the flour, cocoa, baking powder, baking soda, and salt.
In a large bowl whisk the brown sugar, eggs, and vanilla until smooth.
In a small bowl add the finely chopped chocolate and butter. Microwave at half power stirring often, until melted.
Whisk the chocolate mixture into the egg mixture until combined. Fold the flour mixture into the chocolate and egg mixture until just combined and no flour streaks remain. The dough will be fairly soft.
Place the granulated sugar and powdered sugar in two separate small bowls.
(See note #1) Portion the chocolate cookie dough into 2 T. size balls. Drop the balls into the granulated sugar and roll to coat, then roll the dough balls in the powdered sugar to coat. Place the sugar and powdered sugar covered balls on the baking sheet. Repeat until all of the cookie dough has been used.
Bake cookies 1 tray at a time for 10-12 minutes. Cookies will look raw between the cracks and appear undone, but that’s normal.
Remove the cookies from the oven and let cool for 5 minutes on the baking sheet, then transfer to a wire rack to cool completely.