In a large bowl, beat together room temperature butter, brown sugar, and granulated sugar. Beat until ingredients are completely smooth and combined, and light and creamy. Add in the egg and vanilla extract and mix until combined.
In a separate bowl, whisk together the baking soda, salt, unprepared pudding mix, unprepared cake mix, and flour. Stir until combined.
Add the dry ingredients to wet. Beat till combined, but do not overmix. The cookie dough gets very thick. Gently fold sprinkles and chips into the dough with a spatula.
Form tall cookie dough balls that are about 3 tablespoons in size. Cover and chill for at least 1 hour.
Preheat the oven to 350℉. Line a baking sheet with parchment paper or a silicone baking mat.
Place no more than 6 cookie dough balls on a pan to give ample room for the dough to spread while baking. Bake for 9–13 minutes or until lightly browned at the edges and slightly under-baked in the center. I bake mine for about 11 minutes.
Remove from the oven and cool on the sheet pan for another 3–4 minutes. While they are on the sheet pan, you can add a few more chocolate chips and sprinkles to the top, but this is optional. Place cookies on a cooling rack until fully cooled. Cookies are best enjoyed the same day they're made.
Notes
Storage: Once cooled, you can store any leftover cookies in an airtight container at room temperature.