In a medium saucepan, mix together the sugar, heavy whipping cream, butter and salt and bring to a boil. Reduce the heat to medium-low and let the mixture simmer for about 2 minutes, whisking occasionally.

Remove the saucepan from the heat, add the vanilla extract (be careful, the mixture is hot) and stir. Let mixture cool in the pan for 2 minutes, then pour into a jar. Let cool to room temperature and refrigerate until ready to use (up to 5 days). Warm it up in the microwave before using.