Preheat oven to 350 degrees. Combine cake mix, sprinkles, white chocolate chips, oil, egg, and milk in a bowl until the batter is just combined.
Place the batter in a greased 8x8 inch pan. The batter will be thick almost like cookie dough. Bake for 20 minutes or until the edges are slightly golden.
Let them cool for about 20 minutes so the gooey center can set.