In a medium saucepan, combine sugar, butter, and vanilla bean over medium-high heat. Bring to a boil, stirring frequently. Stir in cream, and remove from heat. Add salt and lemon juice, stirring to combine. Store refrigerated, in an airtight container, for up to 1 week. Reheat, in a heatproof bowl set over a pan of simmering water, before using.