Line 2 baking sheets with parchment paper. Set aside.
Preheat your oven to 325 degrees F
In the bowl of a stand mixer with the paddle attachment, cream together butter, sugars, vanilla, and salt until light and fluffy - about 2 minutes.
With the mixer on low speed, add in sifted cocoa powder and baking soda. Scrape down the sides of the bowl.
Add in the egg and mix until incorporated. Scrape down the sides of the bowl.
Turn the mixer to low speed and mix in flour.
Scrape down the sides of the bowl. Fold in white and semi-sweet chocolate chips using a spatula
Shape into 1 tablespoon size balls and place on baking sheet approximately 2 inches apart.
Bake for 13 minutes. Allow to cool on baking tray before transferring to cooling rack
Over baking these cookies will result in dry cookies.