Add egg and continue mixing, scraping sides as necessary.
Add in the cake mix and beat until combined.
Stir in extra sprinkles.
Chill dough for at least 1 hour.
Preheat oven to 350 degrees F.
Form dough into 1-inch balls and roll in powdered sugar. Place on baking sheet 2 inches apart and bake for about 10 minutes.
Allow to cool on baking sheet for 2-3 minutes and then transfer to wore rack to cool completely.