Begin by making the pumpkin gelatin. Place the pumpkin puree, water, pumpkin pie spice, vanilla extract in a medium bowl. Whisk until combined. Sprinkle the gelatin on top and stir to combine. Set aside while the gelatin sets up.
Meanwhile, prep the baking dish you'll use. Use a 9x13" pan for slimmer marshmallows, or a 9x9" pan for thick marshmallows. Grease your pan and grease a rubber spatula. Set aside.
Make the syrup by placing the brown sugar, maple syrup, and water into a large pot over medium heat. Stir to combine, then don't stir for the rest of the time. Let the mixture cook until it reaches 240-245F, about 10-20 minutes.
When the mixture reaches 240-245F, pour it into the bowl of a stand mixer. Let it cool for 1 to 2 minutes, then add the set up gelatin mixture in. Use the whisk attachment to mix for 7-10 minutes, until the mixture has turned a lighter white color and is pulling away from the bowl.
Immediately transfer the mixture to the prepared pan, then work quickly to spread it evenly in the pan with the greased rubber spatula.
Cover the pan with tin foil and transfer to the fridge for at least 2 hours to set up. Or leave it on the counter overnight to set up.
Once set, combine the powdered sugar and cinnamon in a small bowl and stir to combine. Dust the top of the marshmallows with the powdered sugar + cinnamon, then use your fingers to evenly spread it across the surface.
Dump the marshmallows onto a cutting board. Dust the side that is now facing up with the cinnamon + powdered sugar mixture. Lightly grease a large knife then use it to cut the block of marshmallows into smaller pieces. Once cut to your desirable size, quickly toss each on in the bowl of powdered sugar + cinnamon to make sure all the sticky edges are coated. Shake off the excess. Enjoy!!
Keep any leftover marshmallows in an airtight container on the porch. Marshmallows will stay fresh for several days.