In a saucepan on the stovetop, whisk together the sugar, cornstarch, water and lemonjuice until the mixture is not lumpy. Cook over a low to medium heat and stir occasionally until the mixture begins to thicken. Stir constantly once the mixture is thickening. Remove from heat when the sauce is the consistency you desire.

Remove from heat.

Add in the butter and stir until melted

Can be stored in the refrigerator in an airtight container.