In a small saucepan, mix together the sugar, corn flour and salt until well combined.
Whisk in boiling water and bring to a boil over medium heat. Once boiling, allow to boil for 2 minutes to thicken, then remove from heat and stir in butter and vanilla.
Use warm or at room temperature.
Notes
You whatever sugar you want depending on what color/flavor you want the sauce to be. *For those who can have dairy, and want a richer, creamier and thicker sauce, replace the boiling water with hot milk