Pumpkin Spice Rice Crispie Treats
- Butter a 9x13-inch baking dish (or a smaller dish — see Note below).
- In a heavy saucepan or Dutch oven, melt butter over medium-low heat. Add the pumpkin puree and continue to cook until it is warmed through. Fold in 10 ounces of the marshmallows, stirring frequently until almost completely melted. Stir in vanilla, cinnamon, allspice, nutmeg, and salt, and remove from heat.
- Allow the marshmallow mixture to cool 10 minutes; fold in the remaining cup of marshmallows. Continue to cool the mixture for another 20 to 25 minutes until it is room temperature (failure to cool the mixture will result in soggy rice crispy treats.) Add the puffed rice cereal and stir, using a silicone spatula, until combined.
- Press the mixture into the greased rectangular baking dish. Let set for 30 minutes before cutting and serving.