In a saucepan, over medium heat, add sugar and the other ½ cup of cold water and allow it to heat up.
Mix ½ cup of cold water with gelatin and set aside.
Once well combined and heated up, add in the gelatin mixture and bring it to a boil. Stir continually to prevent burning.
Once boiling, remove from heat and mix in salt and vanilla extract.
Transfer the hot mixture into a mixing bowl and whip it on low to cool the mixture off. As it cools it will lighten in color.
Once cooled, and lighter in color, turn the mixer up to full speed and whip until white and fluffy.
Use right away as marshmallow fluff, or pour into sealable glass jars.