3 tablespoons unsalted butter
1/4 cup canned pumpkin puree (100% pure pumpkin. NOT pumpkin pie filling)
1 (10 ounce) bag mini marshmallows plus one cup
1/4 teaspoon pure vanilla extract
1/4 teaspoon ground cinnamon
Pinch of allspice
Pinch of freshly grated nutmeg
Pinch of sea salt or kosher salt
6 cups crispy rice cereal
Butter a 9×13-inch baking dish
Melt the butter in a sauce pan over medium- low heat. Add the pumpkin to the melted butter and continue to cook until it is warmed through, stir to combine. Fold in 10 ounces of the marshmallows, stirring frequently until almost completely melted. Stir in vanilla, the spices, and salt. Stir to combine and remove from heat. Set aside to cool for about 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. Cooling the mixture keeps the rice crispy treats from getting soggy. Add in the cereal and stir, making sure the mixture is combined. I don’t use a spoon for this, I use a spatula or whisk.
Press the mixture into the greased rectangular baking dish. Let set for 30 minutes before cutting and serving.