In a small, heat-proof bowl, microwave the chocolate until completely melted. Set aside.
In a medium mixing bowl, whisk the flour, cocoa powder, baking soda, baking powder, and salt.
In a large mixing bowl or the bowl of a stand mixer, beat the butter and sugars. Add the melted chocolate, milk, and vanilla and beat until combined.
Add the dry ingredients to the wet. Mix to combine.
Form the dough into a ball and wrap in plastic wrap. Refrigerate for at least 1 hour.
Preheat oven to 350°F and prepare two lined baking sheets.
Drop 1.5 tbsp balls of dough onto the baking sheets. Bake for 9-11 minutes.
Once cooled, dust with powdered sugar, if desired. Enjoy!