In a large saucepan, melt 1 stick of butter. Add corn syrup and marshmallows. Stir in cake batter, pudding mix, vanilla, and 1/2 cup white chocolate chips. When chocolate chips are melted, stir in rice krispies. Press mixture into a greased 8x8 pan.
Melt 1 cup white chocolate chips in a saucepan over medium heat. When completely melted, pour over rice krispies. Scatter sprinkles over top. Allow to cool completely, cut and serve.