Butter a 13X9 baking dish

using a heavy saucepan melt butter over medium heat

fold in pumpkin puree and cook until warmed through

fold in 10oz (1 bag) minimarshmellow stirring frequently until almost completely melted

stir in vanilla, cinnamon, allspice, netmeg, salt, and remove from heat

allow to cool 10 minutes and fold in remaning cup of mini marshmellows

cool 20-25 minutes (to room temperature) and add rice krispie cereal using silicone spatula

press into greased baking dish and let sit 30 minutes before serving