Preheat oven to 350°. Line an 8x8 pan with parchment paper and spray it uniformly with cooking spray.  Mix gingersnap crumbs and butter in a small bowl with a fork. Press into the bottom of the pan and bake for 8 minutes. Let cool.

Put the 1/4 cup cold water and the gelatin in the bowl of a stand mixer.  Allow to sit and bloom while you make the sugar mixture.

Meanwhile, combine the sugar, corn syrup and water in a saucepan over medium-high heat.  Stir, then bring to a boil and do not stir anymore! Heat to 250°F registers on a candy thermometer.

In a separate bowl, stir together pumpkin and pumpkin pie spice.

Attach the mixing bowl to a stand mixer fitted with the whisk attachment and start the mixer on low speed.  Carefully pour the boiling sugar mixture down the side of the mixing bowl.  Increase the speed to medium high and add the salt.  Mix until stiff, shiny and white, about 4-5 minutes.  Scrape down the sides of the mixing bowl occasionally with a rubber spatula. (The mixture will be very sticky.)

Turn off the mixer. Add the pumpkin and stir with a spatula as much as possible. Turn the mixer back on medium-high and mix for another 2-3 minutes.  You can test to see if it is ready if you dip a spatula in the mixture and it should form a continuous ribbon off the spatula into the bowl.

Pour the mixture over the crust.  Let it sit at room temperature for at least 8 hours.

Place some powdered sugar in a small bowl. Sprinkle the top of the marshmallows and your knife with powdered sugar. Cut into squares, dipping the top and sides in the powdered sugar to reduce the stickiness. Store in an airtight container.