Grease a shallow baking dish and set aside.
Soften the gelatin in 3/4 cups of water using an electric mixer and let sit for at least 5 minutes.
In medium size saucepan, mix remaining water, granulated sugar, powdered sugar, corn syrup and salt. Then bring to a boil on high heat.
Cook until the mixture registers 240 degrees on a candy thermometer.
Remove from stove and carefully pour mixture into mixing bowl with gelatin.
Beat for 15 minutes until fluffy and thick. Then add vanilla.
Transfer to greased baking dish and let sit for 8 hours uncovered and at room temperature.
Once solidified, cut into desired shape. Pour powdered sugar on surface and coat the marshmallows so they aren't sticky.