Combine flour, cocoa powder, baking powder, baking soda, and salt in a bowl. Set aside.
Beat butter, granulated sugar, and brown sugar in large mixer bowl over medium speed until smooth and creamy. Scrape down the sides and bottom of the bowl as needed.
Add milk and vanilla; mix until incorporated.
Reduce speed to low and gradually beat in flour mixture until combined.
Stir in white chocolate.
Use a small cookie scoop (1.5 to 2 tablespoon) to measure out the cookie dough. Roll each portion into a smooth ball and place on a cookie sheet or large plate. Refrigerate for at least 1 hour up to 2 days. NOTE: I prefer to chill the dough overnight. The colder the dough, the thicker the cookies.
Preheat oven to 350° F. Line a large baking sheet with parchment paper or silicone baking mat.
Place the cooled cookies balls evenly spaced, about 2 inches apart, on your prepared cookie sheet. Optional: If desired, you can add a few more chocolate chips on top of each dough ball.
Bake for 10-12 minutes, or until the edges appear set but still soft in the middle. When you remove the cookies from the oven, they will still look doughy and that is okay they will continue to set as they cool.
Cool on baking sheets for 2 minutes; remove to wire racks to cool completely.