Preheat the oven to 350°F (180°C). Line a baking tray with parchment paper. Set aside.
Add the butter, white granulated sugar and light brown sugar to the bowl of your stand mixer and cream them together until smooth.
Add milk and vanilla extract and mix in.
In a separate bowl add flour, cocoa powder, baking soda and salt and whisk together.
Add dry ingredients to wet and mix by hand (don't use your stand mixer for this part) into a thick cookie dough.
Add chocolate chunks and mix in.
Roll the dough into balls and place evenly onto the parchment lined baking tray. Aim to get 20 cookies.
Bake for 12 minutes at 350°F.
As soon as they come out the oven, press chocolate chips directly into the tops of the cookies while they're still warm and soft from the oven. Leave the cookies to cool directly on the baking tray.