Generously spray a bundt pan with nonstick cooking spray.
Place the popcorn in a large bowl.
Melt the marshmallows and butter together in a large bowl in the microwave or over medium heat on the stove. Stir until smooth. Stir in the dry cake mix.
Immediately pour the marshmallow mixture over the popcorn and stir until the popcorn has been coated with the mixture. Stir in the semi-sweet chocolate chips and the white chocolate chips.
Pour the popcorn into the prepared bundt pan. With buttered hands, press the popcorn into an even layer.
Let it cool slightly, then turn it out onto a serving plate or dish.
Notes
*Duncan Hines cake mix makes a more red cake than other brands that I've tried.If you are worried about the risk of bacteria from the cake mix, you can either stir it in the marshmallow mixture earlier so that it can get hot enough to "cook" the mixture, or you can spread the cake mix on a baking sheet and heat treat it by baking it for 5 minutes at 350ºF.Nutrition information provided as an estimate only. Various brands and products can change the counts. Any nutritional information should be used as a general guide.