Spray a 9x13 baking dish with non-stick cooking spray and set aside.
In a large pot, combine the marshmallows and butter and melt on low heat, stirring every few minutes.
Once the marshmallows and butter have melted stir in the 2 tbs. of canned pumpkin, 2 tsp. of cinnamon and the pinch of nutmeg. Stir well.
Remove the pot from the heat and stir in the 6 cups of Rice Krispies making sure to coat them well.
Pour the mixture into a 9x13 baking dish and use the back of a large spoon or a piece of wax paper to flatten in the pan. Cover and let cool. Cut evenly into squares.
Store in an airtight container.