Line an 8 inch square pan with foil or parchment paper. Spray with cooking spray and set aside.
In a medium saucepan, melt the white chocolate chips and condensed milk over medium-low heat until the chips are almost melted.
Stir in the butter and cake batter flavour until completely melted.
Spread the fudge evenly into the prepared pan.
Sprinkle the top with rainbow sprinkles.
Tap the pan on the counter a few times to make sure the sprinkles attach to the fudge.
Cover and refrigerate for 2-3 hours, or until firm.
Remove from the pan and cut into 25 squares.