Preheat your oven to 350 degrees. Spray a 8x8 inch baking dish with cooking spray and set aside.
In a large mixing bowl combine cake mix and sprinkles in a bowl and give it a quick stir. Add in oil and egg and start to mix everything together. Slowly add in milk a little bit at a time, continue to mix the batter adding a little more milk if necessary. Once everything is combined and you have a thick batter fold in the white chocolate chips if you're using them. Spread cake batter into the baking dish and spread it out evenly with a spatula.
Bake for 25 to 30 minutes, edges will be light golden brown and the center will still looked underbaked. Allow to cool for at least 20 minutes so they blondies have time to set.