Preheat oven to 325 degrees. Line a baking sheet with parchment paper or spray with non-stick spray and set aside.
In a medium-sized bowl or zip-top bag whisk together all dry ingredients: flour, cocoa powder, baking powder, and salt; set aside.
In a large microwave-safe bowl, combine the chocolate chips and butter. Heat them in the microwave on low-power for 20 second increments, mixing each time until butter and chocolate are fully melted. Let cool for 5 minutes.
Use a hand mixer to beat in both sugars to the melted chocolate mixture. Add in the eggs one at a time, mixing to incorporate each one. Add in peppermint extract and milk beating until incorporated.
Add the dry ingredients into the wet ingredients, and stir to combine with a spatula so you don't over-mix. Fold in chocolate chunks mixing until just combined.
Use a cookie scoop to measure batter, shape into uniform balls, and place onto the prepared baking sheet. *Batter will be sticky*
Bake for 7 minutes. Pull the tray from the oven and use the back of a measuring cup to slightly flatten the cookies. Press additional chocolate chunks to the tops of each cookie. Return to oven and bake for another 3 minutes or until the cookies are set but a little gooey in the middle.
Allow cookies to cool on the tray.