In a bowl, combine gelatin with 1/2 cup cold water and let it sit.
In a saucepan, mix sugar, corn syrup, salt, and the remaining 1/2 cup of water. Heat until the sugar dissolves.
Bring the mixture to a boil and let it reach 240°F (115°C) on the candy thermometer.
Slowly pour the hot syrup into the gelatin mixture, beating continuously.
Add vanilla extract and continue to beat until the mixture becomes thick and glossy
Transfer the marshmallow mixture into a parchment-lined baking pan, smoothing the top.
Let it set for at least 4 hours or overnight.
Cut into squares, coat with powdered sugar, and enjoy!