Preheat oven to 350℉ and line baking sheet with parchment paper. In the bowl of a stand mixer, use the paddle attachment to beat together melted and cooled butter, sugar, brown sugar, and unsweetened cocoa until well combined and resembles brownie batter.
Beat in eggs and vanilla, scraping sides of bowl as needed.
In a medium-sized bowl, whisk together flour, salt, and baking soda. Add to mixer, mixing just until combined. Add chocolate chips and M&M candies and give a final stir to combine.
Use a standard-size cookie dough scoop to measure cookie dough and place on baking sheet. Top with additional M&M'S and chocolate chips. Bake for about 10 minutes.
Optional Step: When taking the cookies out of the oven, immediately use a large cup to make perfect cookie circles. To do this, place the cup upside down over the cookie and quickly spin the cookie inside the rim of the cup. This will even out the edges of the hot cookie and make it into a perfect circle. Work quickly because this tip works best straight out of the oven.