In medium size pot bring water to a boil.
Once boiling add in the sugar and cornstarch.
Stir constantly for 3-5 minutes.
Remove from heat. Add in butter, salt, and vanilla.
Stir until butter is completely melted.
Allow to cool prior to using.
Keep refrigerated for up to one week. Syrup may separate, simply bring to room temperature and high in microwave for 30 seconds on medium power, stir until re-incorporated fully.