In a medium sized, heavy-bottom saucepan melt the butter over medium heat. When melted, stir in the brown sugar til it's starting to dissolve. Then add in the salt & and whipping cream and stir until dissolved.

Bring the mixture to a slow, gentle, rumbling boil and allow to bubble for approximately 5 minutes while stirring occasionally to ensure the mixture isn't burning. Remove the pan from the heat and stir in the vanilla.

Serve warm over ice cream, or allow to cool completely and store in an airtight container in the fridge.