For the pomegranate jelly: In a medium saucepan, stir together sugar and cornstarch. Whisk in cold water until smooth. Stir in pomegranate arils and place over medium heat. Use a potato masher to break arils while heating. This should take around 5 minutes. Bring mixture to a boil to thicken. Remove from heat and strain jelly to make it seedless. Set aside to cool. As the jelly cools, it should thicken more.