Heat butter in a large bowl in the microwave for 60 seconds at 50% power until butter is very soft but not melted.
Whisk in granulated and brown sugars.
Whisk in eggs, then vanilla.
Whisk in black cocoa powder.
In a separate bowl, whisk together flour, baking powder, baking soda, and salt.
Stir dry ingredients into the wet mixture with a sturdy wooden spoon.
Stir in chocolate chips.
Chill batter for at least 30 minutes.
While batter is chilling, preheat oven to 350°F.
Use a slightly overfilled 1 ½-tablespoon cookie scoop to scoop out cookie dough, then roll into balls with your hands. Place on a parchment-lined baking sheet at least 2 inches apart.
Bake for 10 minutes, until cookies look firm and no longer glossy on top.
Remove baking sheet from oven.
Let cookies sit for 2 minutes, then remove and let cool on a rack.
Notes
Storage Tips: Store in an airtight container at room temperature for up to 4 days. You can also freeze cookies in a ziplock freezer bag for up to 3 months.Expert Tips: Whisking black cocoa powder into the liquid mixture rather than the dry mixture helps it incorporate better into the cookie dough.As with all baking recipes but particularly with this one, I highly recommend weighing your ingredients for best results. Measuring cups, and how tight you pack them, really vary in how much flour or sugar is in them. These cookies have a tendency to spread if you play fast and loose with your measurements.Don’t skip the chill time. Cookie dough made with black cocoa powder is soft, and the chill time ensures you don’t get flat cookies.It’s difficult to tell when cookies made with black cocoa powder are done since you can’t look for golden edges. Baking 1 or 2 in a test batch in your oven to make sure you know exactly how long to leave them in may be a good idea.