Funfetti® Gooey Bars

Preheat oven to 350 degrees F (175 degrees C). Line a 9x9-inch pan with aluminum foil and spray liberally with cooking spray.

Mix yellow cake mix, butter, and egg together in an electric stand mixer fitted with the paddle attachment until a thick dough forms, add 1/3 cup multi-colored sprinkles and mix to incorporate.

Press 2/3 of the dough into bottom of prepared pan; sprinkle white chocolate chips and remaining 1/3 cup multi-colored sprinkles over top, followed by sweetened condensed milk. Roll remaining 1/3 of the dough into balls and arrange evenly over top of contents in baking dish, pressing down to flatten.

Bake in preheated oven until it just begins to brown, about 30 minutes. Cool completely on wire rack before cutting, about 1 hour.