Line two cookie sheets with parchment.
In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment (or in a large mixing bowl, using a handheld mixer), cream together the butter and both sugars on medium-high speed for 3 to 5 minutes, until light and fluffy. Scrape down the bottom and