Heat butter, brown sugar and cream in a pot on the stove top, stirring until melted and smoothed. Bring to a boil and then turn down to a simmer for 3-5 minutes. Remove from heat and add vanilla and salt to taste. Start with 1/4 teaspoon salt and add more if desired. Can be left at room temperature, or if storing overnight or longer, place in a covered container in the fridge. Reheat gently in the microwave.