Line a 9x13-inch baking dish with plastic wrap and spray it uniformly with nonstick cooking spray. Set aside.
Put the 1/2 cup cold water and the 3 envelopes of gelatin in the bowl of a stand mixer. Allow to sit and bloom for 10 minutes.
Meanwhile, combine the sugar, corn syrup, and 1/4 cup water in a saucepan over medium-high heat. Bring the mixture to a boil. Once it has started boiling, do not stir. Bring the mixture to 250ºF. (If you don’t have a thermometer, you will know it is at the right temperature when a small amount of the syrup dropped into a glass of cold water forms into a rigid ball.)
In a separate bowl, combine the pumpkin, cinnamon, ginger, nutmeg, and allspice. Mix well.
Place the mixing bowl on a stand mixer fitted with the wire whip attachment. Turn to low speed. Carefully pour the boiling sugar mixture down the side of the inside of the mixing bowl. Increase the speed to medium and add the salt.
Let the mixture mix until it is shiny and white, about 10-12 minutes, scraping down the sides of the bowl with a rubber spatula occasionally.
Remove the bowl and fold in the pumpkin mixture until combined. Return the bowl to the stand mixer and mix for 3 more minutes. You will know when the mixture is done when you dip a spatula into the mixture and it forms a continuous ribbon as it drips off the spatula into the bowl.
Pour the mixture into the prepared pan. Let it sit at room temperature for at least 8 hours.
Place the graham crackers in a food processor and process until you have fine crumbs.
Lay a piece of wax paper or parchment paper on a cutting board and spread half of the crumbs onto the paper. Put the other half of the crumbs in a small bowl.
Turn the pan of marshmallows over onto the crumbs, then remove the plastic wrap. Cut the marshmallows into squares. Dip each of the marshmallows in the graham cracker crumbs until all sides are covered.
Notes
These marshmallows are best fresh, but can be kept in an airtight container for about a week, or frozen for up to a month.Nutrition information provided as an estimate only. Various brands and products can change the counts. Any nutritional information should be used as a general guide.