Combine cornstarch and powdered sugar.
Line 8x8 pan with parchment paper, and cover the bottom and sides with half of the cornstarch mixture.
Put gelatin and first 1/2 cup water into the bowl of a stand mixer and set aside.
Heat sugar, maple syrup, corn syrup, salt, and the other 1/2 cup of water covered over medium-high heat for approximately 4 minutes.
Uncover and continue heating until the mixture reaches 240 F.
Remove from heat.
Begin beating the gelatin mixture with the whisk attachment of the mixer, and very slowly pour in the syrup mixture.
Increase the mixer to high speed (do this slowly to avoid splatter!) and beat an additional 13 minutes.
Spread the marshmallow mixture into the prepared pan. Sprinkle remaining cornstarch mixture over top of the marshmallow mixture.
Let set for 4 hours.
Cut into cubes with a greased knife, or use a greased cookie cutter to cut into shapes.