Dissolve jello in water then stir in sugar, keep stirring until sugar is dissolved as well
Add in corn syrup and stir well
Chill for 20-25 minutes then beat until stiff
Pour mixture onto a wax paper lined mold or parchment paper sprinkled with icing sugar
Chill overnight
Take out mold from fridge and dump marshmallow on icing sugar lined parchment paper on a cutting board
Coat marshmallow with icing sugar and slice