Place one stick of butter on the kitchen counter to soften. Place the other stick of butter in a microwave safe bowl and melt completely in the microwave. Allow the butter to cool to a semisoft texture either on the counter or in the refrigerator, about 30 minutes.
In the bowl of a stand mixer fitted with the paddle attachment, cream the softened butter, microwaved butter, and both sugars until fluffy. Add vanilla and eggs and mix briefly until just incorporated.
In a separate bowl, whisk together cocoa powder, flour, baking soda, and salt. Add the flour mixture to the butter mixture and combine until you cannot see any more dry flour. The dough should be sticky but you should be able to touch it with your hands without it being too messy. Stir in chocolate chips.
Cover the top of the bowl tightly with plastic wrap and allow the dough to rest in the refrigerator for 30 minutes or up to 2 days.
When you're ready to bake the cookies, preheat the oven to 350ºF. Roll the dough into balls slightly larger than a golf ball and place two inches apart on a baking sheet lined with parchment paper or a Silpat. Bake 8-9 minutes, depending on how cold your dough is. The cookies should be puffy and soft. Allow to cool on the baking sheet for 5-10 minutes before transferring to a cooling rack to cool completely (or be devoured).