Line a 8x8 inch cake pan with parchment paper and butter or spray with cooking spray.
Pour water in the bowl of stand mixer and sprinkle the gelatin over it to bloom. Set aside while you prepare the rest.
Add sugar, eggnog, maple syrup to a medium saucepan and clip candy thermometer to it.
Heat mixture over medium heat and stir until sugar dissolves. Once sugar dissolves, cook without stirring until candy thermometer reaches 240 degrees, usually about 8-10 minutes.
Once it reaches 240 degrees, turn the stand mixer on low and slowly add the hot sugar mixture to the mixer bowl.
Turn the mixer to high and beat until the mixture becomes thick and fluffy, about 10 minutes.
Add vanilla and mix until combined.
Pour the mixture into the prepared pan and smooth out with an oiled
Set aside for 8 hours or overnight, uncovered.
Mix together powdered sugar and cornstarch.
Butter a serrated knife and cut marshmallows into squares.