Preheat oven to 325 degrees F. Line 2 baking sheets with parchment paper or prepare sheets with cooking spray and a light dusting of flour.
Whisk together flour, cocoa powder, baking powder, baking soda and salt.
Whisk together brown sugar, eggs and vanilla in a big bowl.
In a small bowl, combine baking chocolate and butter. Microwave in 20 second increments, stirring between each, until it's melted and combined.
Whisk the chocolate and butter into the egg mixture until combined. Stir into the flour mixture until it's all well-mixed.
Let the dough sit at room temperature for 10-15 minutes.
Place granulated sugar into a shallow bowl, and the powdered sugar into another shallow bowl.
Take a cookie scoop or 2 tablespoon of dough and roll into balls. Roll each ball in granulated sugar, then in powdered sugar until they are covered in both. Place the dough balls evenly on the prepared cookie sheets.
Bake the cookies for 10-12 minutes, rotating baking sheet half-way through. Bake until they are puffed and cracked. Your edges will look set, but be very soft in the middle. It might look like they aren't done yet, but they probably are!