1.Place butter, brown sugar, heavy cream, salt, and molasses into a small saucepan over medium heat and let the sugar dissolve completely. Resist the temptation of mixing too much. Instead, hold the pan and gently swirl the sauce in a circular motion until everything has dissolved.
2.Bring to a boil. Once everything has dissolved and the sauce begins to turn a darker color, stir to prevent burning. The whole process will take about 5 – 7 minutes until thickened.
3.The sauce is ready when it has thickened enough to coat the back of a spoon and turned a dark brown color. Remove from heat and add the vanilla extract, mix and combine. Allow to cool before storing. The sauce will thicken even further as it cools.