Preheat the oven to 350°F and line 3-4 baking sheets with parchment paper.
In a medium-sized mixing bowl, whisk together the flour, cocoa powder, salt, and baking soda.
To a large mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, add the butter, sugar, and brown sugar. Beat until light and fluffy. Add the milk and vanilla and beat again until creamy.
Add the dry mixture to the wet and mix until well combined.
Fold in the chocolate and white chocolate chips.
Scoop out 1.5 tbsp-sized balls of dough and place on the baking sheets, leaving room in between for spreading.
Baking two sheets at a time, bake for 9-11 minutes. Allow to cool on their pans, then enjoy!