Preheat oven to 350 degrees Fahrenheit.
In the bowl of an electric mixer cream together the butter and sugars on medium speed for 1-2 minutes.
Add the egg yolk and mix until combined, about 30 seconds
Whisk together the flour, cocoa, baking soda and salt. Add to the butter mixture and beat on low until just combined.
Place the sprinkles in a bowl.
Using a tablespoon size scoop the batter and roll into a ball.
Optional – Place each ball of dough into the sprinkles and roll around until the dough is entirely covered with sprinkles.
Place on a baking sheet lined with parchment paper 2” apart.
Bake for 11 minutes or until the cookies are set. Remove them from the oven and rap the sheet once on the counter. This will flatten the cookie and create the crackly top.
Allow the cookies to cool on the pan for 10 minutes. Place the cookies on a wire rack to cool completely.
This recipe can be doubled.
Makes about 18 cookies.