In a large bowl combine sweetened condensed milk, pumpkin puree, melted butter, vanilla, and pumpkin pie spice.
Whisk until all ingredients are throughly incorporated.
Stir bite sized graham crackers into the pumpkin mixture.
In a chilled bowl, pour in your cold whipping cream and use your stand mixture to whisk the heavy whipping cream until stiff peaks form. (Look at photos above for what that looks like.)
Gently fold the whipped cream into the pumpkin mixture.
Place 1/3 of the pumpkin mixture into the bottom of an airtight container.
Pour 1/2 of the melted marshmallow fluff to cover the bottom layer of the pumpkin mixture.
Top with another 1/3 of the pumpkin mixture.
Top that with the last of the melted marshmallow fluff.
Pour the remaining pumpkin mixture into the airtight container.
Freeze for 4-6 hours or until set.