In a medium sized bowl, whisk together the flour, cocoa powders, baking soda, and salt. Set aside. 

In the bowl of a standing mixer fitted with the paddle attachment, beat the butter on medium speed until smooth and creamy. Add sugars and beat on medium-high speed until light and fluffy. Add egg and vanilla, mixing until combined. Use a rubber spatula to scrape down the bottom and sides of the bowl as needed. 

Gradually add the dry ingredients, mixing on low speed. Increase to high speed and mix in the milk. Mix in the chocolate chips. until evenly distributed. Cover dough tightly with foil, plastic wrap, or Glad Press'n Seal. Let chill in the refrigerator for a few hours or overnight. 

Remove cookie dough and let it warm up to room temperature for 20 – 30 minutes. 

Preheat oven to 350F. Line two baking sheets with parchment paper or silicone baking mats. Set aside. 

Scoop a heaping tablespoon of dough and roll into a ball. Place on prepared cookie sheet. Repeat with remaining dough, placing additional chocolate chips on top if desired. Bake for 10 minutes. Remove from oven and let rest on cookie sheet for 5 minutes. Transfer to wire rack to continue cooling.