1. Spread the pumpkin puree over a paper towel to soak excess moisture out of the pumpkin.
2. In a large stock pot, heat the butter over medium heat. When the butter is melted, add the mini marshmallows and stir until they begin to melt.
3. When the marshmallows are melted, remove from heat and stir in the pumpkin and pumpkin pie spice until well combined.
4. Add the Rice Krispies and stir until evenly coated.
5. Press the mixture into a 9x13 dish and allow to rest for at least one hour before cutting and serving.