Preheat The Oven & Prep Your Pans. Start by preheating the oven to 350 degrees F. Line two cookie sheets with parchment paper.
Mix The Dry Ingredients. In a medium bowl, combine gluten-free flour, cocoa powder, baking soda, and salt. Whisk until it’s well blended and set aside.
Cream Butter & Sugars. In the bowl of a stand mixer (or a large mixing bowl), combine softened butter, brown sugar, and sugar. Cream with a paddle attachment or hand mixer 2-3 minutes, or until smooth, light, and fluffy.
Add Eggs & Vanilla. Scrape down the edges of the bowl, and add eggs one at a time, beating to combine fully before adding the next one. Add vanilla extract and stir to combine.
Slowly Add Dry Ingredients & Milk. Add about half of the dry ingredients a little at a time, and mix until almost fully combined. Add the milk and mix for a few seconds, then add the second half of the dry ingredients and mix until almost fully combined (just a little powder left).
Mix In Chocolate Chips. Pour in 1/2 cup dark chocolate chips, 1/2 cup white chocolate chips, and 1/2 cup semi-sweet chocolate chips (or milk chocolate chips) and mix until just combined. The dough will be a bit sticky, like thick brownie batter.
Scoop & Bake. Use a large cookie scoop (3 Tablespoon) to scoop 6 cookie dough balls onto a baking sheet. (I like to roll them smooth in my palms first for the prettiest presentation.) Bake cookies 9-11 minutes, or until the edges are set and the centers look just underdone. (I bake mine 9.5 minutes) Shape & Cool. When the cookies are done baking, use a large round cookie cutter to gently coax them into perfect circles, if needed (this is just for looks!), fill in any gaps on the surface with some extra chocolate chips, and cool 2-3 minutes on the baking sheet before transferring to a wire rack to cool completely. Repeat until all the cookies are baked, alternating between cookie sheets each batch so you don't put cool dough on a hot baking sheet. Serve & Store. Enjoy cooled cookies right away and store leftover cookies in an airtight container at room temperature 2-3 days or freeze up to 2 months.