To a large bowl or the base of your stand mixer, add the oil, white sugar, and brown sugar. Using your stand mixer or electric hand mixer, start at a low speed and slowly increase it to high until the oil and sugar are fully combined. Scrape down the sides and bottom of the bowl.
Add the egg and vanilla to the bowl or stand mixer and mix until just combined. Scrape down the sides and bottom of the bowl as needed.
In a medium bowl, whisk together the flour, baking soda, salt, and cocoa powder.
If using a stand mixer, keep the mixer on while you slowly pour the dry ingredients into the wet ingredients. If using a hand mixer, add the dry ingredients into the wet, one cup at a time, mixing after each addition. Beat until just combined.
Fold the chocolate chips into the dough.
(optional) Cover the cookie dough and chill for at least 1 hour, up to overnight. We tested this recipe multiple times and found the cookies back up beautifully without chilling the dough, but if you're making ahead or having trouble with flat cookies, chilling is a great option.
When you’re ready to bake, remove the cookie dough from the fridge and allow it to soften for about 10 minutes. Note: if you’re only refrigerating your dough for an hour, you can skip this step – it should be soft enough to work with as is.
Preheat the oven to 350°F and line two baking sheets with parchment paper.
Using a #40 scoop, scoop the dough, then roll it in a ball with your hands to form the cookie balls. Place the cookies on the baking sheet, leaving 1.5 inches between each cookie.
Bake the cookies for 9 minutes. They are easy to overbake because they’re dark, but know that they’ll harden as they cool.
After about 5 minutes on the baking sheet, move the cookies to a wire rack to finish cooling before serving/storing.