Preheat the oven to 375F. Line 2 baking sheets with silicone baking mats or parchment paper.
In a medium bowl, whisk together the flour, cocoa powder, baking soda, baking powder and salt.
In a large bowl (or the bowl of a stand mixer) add the sugar and butter. Mix with an electric mixer for 1-2 minutes until creamed. Add the egg and mix for another 1-2 minutes, scraping down the sides.
Add the dry ingredients in 3 additions, mixing after each addition. Mix the dough until completely combined. Cover the dough tightly with aluminum foil or plastic wrap and chill for 30 minutes. Chilling is mandatory. If you chill the dough for longer, let it come to room temperature for 15 minutes before scooping.
Using a ½ tablespoon or teaspoon measure, scoop out 1-2 teaspoon size balls of dough. Roll into a ball and place on the lined baking sheet. Flatten the dough balls slightly.
Bake for 6 minutes for soft cookies or up to 8 minutes for crisper cookies. Let cool for 5 minutes then transfer to a wire cooling rack to cool completely.