Spread the pumpkin purée out and press it between paper towels (or a thin cloth) a few times to remove excess liquid. There should be ¼ cup purée (if you have less, press out some more).
In a large pot, melt and brown the butter over medium-low heat. After it foams, it will begin to turn golden brown with a nutty aroma. Stir frequently, watching carefully until it just browns. Be careful not to burn the butter.
Add the pumpkin purée and stir until it's completely combined and heated.
Add the cinnamon, nutmeg, cloves, and vanilla and stir to combine.
Lower the heat and add the marshmallows, stirring until all marshmallows are just melted. Remove from heat and let set for about 5 minutes.
Add the brown rice crisps and fleur de sel, and stir to combine.
Spread evenly in the parchment-lined pan and let rest for 25-30 minutes to cut and serve. Note: it will be very sticky if you try to cut it before it sets properly.
This nutritional information has been automatically calculated, and as such, may be incomplete or inaccurate. Please reference the specific ingredients you use for the most accurate nutritional information.