In a mixing bowl, combine the butter, brown and white sugars. Cream together on high speed for 2-3 minutes until light and fluffy, scraping down the sides of the bowl as necessary.
Add in the eggs one at a time, mixing well in between. Add in the vanilla and mix.
In a small bowl, whisk together the baking soda, salt, cocoa powder, and flour. Add into the wet ingredients and mix slowly until combined and no flour pockets are left.
Add in mini chocolate chips and mix well. The batter will be sticky and very soft. Using a spatula, spread the batter evenly up the sides of the mixing bowl (spreading thin helps decrease chill time).
Cover the dough and chill for 30 minutes. Preheat the oven to 350 °F, and prepare a baking sheet with a silicon baking mat or cooking spray. Sift the powdered sugar into a bowl.
Scoop the chilled dough into balls directly into the sifted powdered sugar and roll around with a spoon, to coat the balls evenly.
Transfer to a baking sheet and bake for 8-10 minutes, or until cookies have spread and have crackled tops. Cool for 10 minutes before serving.
Notes
To store: cool completely and transfer to an airtight container. Store at room temperature for up to 3 days or freeze for up to 3 months.