In the bowl of a stand mixer (or in a large bowl using a handheld mixer), cream butter until smooth.
Add sugar and brown sugar, beat until well-combined.
Beat in egg and vanilla extract.
In a separate, medium-sized bowl, whisk together flour, cake mix, baking soda, and salt.
Gradually stir flour mixture into butter mixture until completely combined.
Fold in sprinkles and mini chocolate chips.
Cover with plastic wrap and chill cookie dough for at least 30 minutes.
Preheat oven to 350F and prepare cookie sheets by lining with parchment paper.
Once cookie dough has chilled, drop by rounded 1 1/2 Tablespoon-sized scoops onto prepared cookie sheets, spacing at least 2" apart.
Bake on 350F for 10 minutes. Allow to cool completely on cookie sheet before enjoying. Cookies will puff in the oven and then settle as they cool.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)