In a small microwave safe bowl, microwave the chocolate and the butter in 30 second intervals, stirring after each, until smooth.
In a separate bowl, stir together the flour cocoa powder, baking powder and salt; set aside.
In a large bowl, beat together the eggs, sugar, brown sugar, milk and vanilla until smooth. Add the melted chocolate and mix again.
Add the flour mixture and stir until just combined. Fold in the chocolate chips.
Cover and chill the dough for at least 1 hour.
Preheat the oven to 350°F (180°C), or 160°C for a fan oven. Line 3 cookie sheets with parchment paper or silicone baking mats.
Using a small cookie scoop (1 ½ tablespoon size), scoop out cookie balls onto the prepared cookie sheet 2 inches apart. Press extra chocolate chips into the top if desired. Bake in the preheated oven for 10-12 minutes or until the cookies have puffed and crackled.
Cool for 10 minutes before transferring to a cooling rack to cool completely.
Notes
Chill the dough thoroughly. This cookie dough will be wet and very sticky when you're finished mixing it. Chilling will allow the butter to solidify again and make the dough easy to handle.
Don't overmix the dough. Overmixed chocolate cookie dough can lead to tough, dry cookies. Stir the flour into the wet ingredients until you can't see any dry streaks anymore, then stop!
Don't overbake. It's hard to tell when chocolate cookies are done because you won't necessarily see them brown or turn golden. Instead, look for the outer edges of the cookies to be dry, and the tops to be just barely set. The center of the cookies will finish cooking while the cookies cool.
Add extras: This recipe calls for 1 cup of chocolate chips. You can use just a half cup of chocolate chips and a half cup of just about anything else! Try these with walnuts, white chocolate chips, or chopped peanut butter cups.
Try some sea salt: A sprinkle of flaky sea salt added to the top of these cookies as soon as they come out of the oven would be divine!
To Store: Keep the cookies in an airtight container at room temperature for up to 5 days or freeze for up to 3 months.