In a medium pot, combine marshmallows, canned pumpkin, spices, and salt.
Heat over medium-low heat, stirring almost constantly, until marshmallows are completely melted and mixture uniform in color, about 6 to 8 minutes.
Scrape mixture into a medium bowl and allow to cool to room temperature, 45 minutes to an hour.
Make the Crust
While your marshmallow filling cools, in a small bowl, combine graham cracker crumbs, melted butter, and brown sugar. Stir together until well-mixed and press crumbs into a 6-inch pie tin in an even layer. Place in the freezer until you’re ready to use it.
Assemble the Cheesecake
Once marshmallow mixture has cooled, in a separate medium bowl, combine heavy cream and sugar. Beat using a handheld electric mixer, starting on low and working up to high, until stiff peaks form (when you lift the beaters straight out, they should leave peaks of whipped cream that stand straight up and don't flop over at the tip). Set aside.
Add softened cream cheese to the cooled marshmallow mixture and beat until the cream cheese is completely incorporated.
Switch to silicone spatula and gently fold the whipped cream into the pumpkin/cream cheese mixture, being careful not to deflate the cream too much as you go.
Once there are no streaks remaining, spoon the filling into your prepared pie crust. There may be some extra filling that won’t fit. You can discard (or eat it).
Smooth the top of the pie and refrigerate until firm, 3 to 4 hours.
Decorate with additional whipped cream and a sprinkle of cinnamon if desired, and enjoy!
Notes
*If you have premixed pumpkin pie spice, you can replace the spices (not the salt) with 1 teaspoon of pumpkin pie spice.Approximate nutritional information is for 6 slices without additional whipped cream.