In a large mixing bowl, beat the room temperature unsalted butter, light brown sugar, and granulated sugar together using an electric mixer until light and fluffy, about 2-3 minutes.
Crack in the large egg and pour in the vanilla extract. Beat until well combined.
In a separate bowl, whisk together the baking soda, salt, instant vanilla pudding mix, Funfetti cake mix, and flour.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Avoid overmixing.
Gently fold in the sprinkles and white chocolate chips until evenly distributed.
Cover the bowl with plastic wrap and chill the dough in the refrigerator for at least 30 minutes.
Preheat the oven to 350°F (175°C) and line cookie sheets with parchment paper.
Use a cookie scoop to portion out the dough onto the prepared cookie sheets, leaving enough space between each scoop.
Bake the cookies for 10-12 minutes until the edges are lightly golden and centers look slightly underbaked.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. Enjoy!