With a hand or stand mixer, cream together the room temperature butter and sugars. Add in the egg and vanilla. Mix together until completely incorporated and smooth.

In a separate bowl, combine the flour, cake mix, salt and baking soda. Sift together. (Try to get as much of the dry ingredients through the fine mesh as possible. Pour out the little flecks of confetti to the sifted dry ingredients.)

Gradually add the sifted dry ingredients to the wet, stopping the mixer to scrape down the sides of the bowl. Batter will be very thick. Stir in the chocolate and white chocolate chips as well as the sprinkles. Pour dough out onto a piece of plastic wrap. Wrap and refrigerate the dough for at least 2 hours or overnight.

Preheat the oven to 350 degrees. Line a baking sheet(s) with a silicone baking mat or parchment paper.

Take dough out from refrigerator. Using a cookie scoop, roll out balls of dough using your hands. Place on prepared baking sheet, arranging 12 to a pan, spaced evenly. Bake cookies for 10-12 minutes or until golden brown on the outside and set in the middle.

Let cookies cool on the baking sheet for 5 minutes before transferring to a rack to cool completely.