Preheat the oven to 350 degrees Fahrenheit. Spray a baking sheet with nonstick baking spray. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter, brown sugar, and granulated sugar until fluffy, about 3-4 minutes.
Add the egg and vanilla. Beat for 1 minute or until combined.
In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt.
Add the flour mixture to the butter mixture, and beat on low until just combined. Do not overmix.
Using a 1 tablespoon cookie scoop, scoop the cookie dough and roll it into a ball using your hands. Then roll in the sprinkles and place them on the prepared baking sheet.
Bake for 11-13 minutes, or until the edges of the cookies are firm.
Remove from the oven and allow to cool for 10 minutes before transferring to a wire rack to cool completely.