Special equipment: a 12-cup Bundt pan
Spray a 12-cup Bundt pan with cooking spray. In a large bowl, combine the caramel popcorn, plain popcorn and macadamia nuts and toss to blend.
Melt the butter in a large pot over medium heat. Add the marshmallows and cook, stirring constantly, until the marshmallows are melted. Pour the popcorn mixture into the melted marshmallows and stir quickly to thoroughly coat all the popcorn. Transfer to the prepared pan and press the mixture with a rubber spatula to compact it. Let sit for 1 hour to set.
With a plastic knife or offset spatula, run it along the edge of the pan to loosen the cake. Turn the pan upside-down onto a serving platter to release the cake. Sprinkle with the gold and silver sprinkles.