Fully cover the inside of an 8x8 or 9x9 pan with aluminum foil or parchment paper. Spray with non-stick spray to coat.
In the bowl of a stand mixer or a large bowl (if you're using a hand mixer) add in the ice water and sprinkle in the gelatin. Stir just a few times to incorporate the powder into the water. (Don't worry about lumps...they'll dissolve later)
Add the Karo light corn syrup, sugar, and water to a sauce pan and heat over medium heat. Stir just until the sugar is fully incorporated then stop stirring all together.
If you're using a thermometer: heat the mixture until it reaches 240° then remove it from the heat. If you do NOT have a thermometer: watch closely and once the entire surface of the mixture is bubbling (see photo above) set a timer for 90 seconds, then remove from the heat.
Turn your mixer on low and VERY carefully and slowly, pour the hot sugar mixture into the gelatin mixture. Once everything is added, you can then mix on medium-high for 12 minutes. It will turn white and become glossy and thick.
Mix together the pumpkin puree, vanilla extract, pumpkin pie spice, cinnamon, and salt. Add this to the marshmallow mixture after the 12 minutes. Beat for just a few more rotations until it's fully incorporated.
Pour the marshmallow mixture into the prepared pan.
Mix together the dusting powder and sprinkle just a thin coating on top of the mixture in the pan. Set aside the majority of the mixture for later.
Allow the marshmallows to set over-night or at least 8 hours.
After the marshmallows have set, lay out a piece of parchment or foil and sprinkle with more dusting powder.
Slice the marshmallows with a sharp knife sprayed with non-stick spray then coat all the edges in the powder.
Store the marshmallows in an airtight container for 3-4 days (If they last that long!)