In a medium mixing bowl, whisk together dry ingredients (flour, cocoa powder, soda, baking powder and salt). Set aside.
Melt chocolate over a double boiler. Set aside to cool to room temperature.
In a large mixing bowl, beat butter for 30 seconds until creamy. Gradually add sugar and beat until light and fluffy (3 to 5 minutes).
Add egg and mix well.
Add melted and cooled chocolate and mix well. Scrape the sides of the bowl if needed.
Add the dry ingredients and mix on low just until incorporated.
Mix all of the ingredients for the sugar mixture in a flat plate.
Scoop the cookie dough using 1,5 tablespoon size scoop, roll in balls and roll in sugar mixture. Place on a plate, cover with foil and refrigerate for at least 30 minutes, preferably overnight.
When ready to bake, preheat the oven to 375 degrees F.
Line a baking sheet with parchment paper or silicone baking mat.
Place cookie dough balls on baking sheets, leaving at least 2 inches of space between them.
Bake for 8 to 9 minutes. No longer than 10 minutes.
Let cookies cool completely on sheets. They will look wet and underdone in the creases. They will finish baking while cooling.