Place butter and chocolate chips in a small, heavy-bottomed saucepan. Set over low heat and cook, stirring often, until everything is melted. Remove from heat and let cool slightly, then whisk in cocoa powder until smooth.

Meanwhile, in the bowl of a stand mixer fitted with the paddle attachment, cream together the eggs, brown sugar, and granulated sugar at medium speed until pale yellow and the mixture ribbons on itself slightly. Add vanilla and mix until combined.

Carefully pour the butter and chocolate mixture into the bowl of the stand mixer on top of the egg and sugar mixture, and mix at low speed until the chocolate has been incorporated.

Add the flour, baking soda and salt and mix at low speed just until only a few streaks of flour remain.

Using a rubber spatula to fold in any remaining flour, then chill for 20 minutes. Meanwhile, preheat the oven to 350˚F and line 2 rimmed baking sheets with parchment paper. Place the powdered sugar in a shallow bowl.

Once chilled, using a 1.5 tablespoon-size spring loaded cookie scoop, scoop 12 dough balls on each prepared baking sheet about 3 inches apart. Roll into even balls, then coat each in powdered sugar. Bake for 8 to 10 minutes, or until the cookies have spread significantly and have crackly tops.

Remove from the oven and let cool for about 1 minute on the baking trays before transferring to a rack to cool completely.