Add brown sugar, heavy cream and salt to a 3-quart saucepan oven over medium-low heat.
Stir together to combine with a wooden spoon or silicon spatula.
Add butter. Allow the butter to melt completely and the mixture to reach a rolling boil
Cook until the caramel sauce thickens, about 5 to 7 minutes.
Remove from heat and stir in vanilla. Allow to cool about 5 minutes and then pour into an airtight container for storing in the refrigerator.
NOTE : To prevent crystallization in your caramel sauce, make sure that your pot and spoon (silicone or wood!) are extremely clean as any debris can cause crystallization. Also, you may add 1 teaspoon of corn syrup to the mixture to prevent any crystallization if you choose.