In a large pot over low heat, melt the butter, stirring until it becomes a golden pool. Gradually add in the mini marshmallows, stirring until fully melted and smooth—about 5 minutes.

Remove from heat and gently fold in the freshly popped popcorn, ensuring every piece is well-coated with the marshmallow mixture—takes about 3-4 minutes.

Allow the mixture to cool slightly for 5 minutes, then fold in the mint chocolate pieces evenly.

Prepare the bundt pan with nonstick cooking spray. Firmly pack the popcorn mixture into the pan ensuring it's compact.

Let the packed mixture rest for 10 minutes, then turn the pan upside down onto a serving platter and tap to release the cake.

Press sprinkles onto the top while warm, allowing the cake to set for another 10 minutes before slicing.

Slice into pieces and serve at room temperature.