Whisk together the flour, cocoa, baking soda, and salt.
In a large bowl beat together the butter and sugars until fluffy.
Add the egg and vanilla and continue mixing until combined. Turn off the mixer and scrape down the sides of the bowl.
Slowly mix in the dry ingredients on low speed until incorporated.
Turn off the electric mixer and stir in the chocolate chips. I usually reserve about ¼ cup of chocolate chips for sprinkling on top.
Cover the bowl with cling film and chill in the refrigerator for at least 3 hours or up to 48.
When ready to bake, preheat the oven to 350F degrees. Line 2 cookie sheets with parchment paper or silicone baking mats. Take the dough out of the fridge for 10-15 minutes to warm up slightly.
Form dough into balls 3 tablespoons in size and place 3 inches apart on baking sheets. (Or form into balls of 1 - 1.5 tablespoons in size and place 2 inches apart).
Bake cookies for 11-13 minutes until the tops are just set (or 8-10 minutes for smaller cookies). Remove from oven and let cool on the tray for 10 minutes before transferring to a wire rack to continue cooling. While the cookies are fresh from the oven, optionally dot the tops of each cookie with a few extra chocolate chips.