In a medium saucepan, melt the butter over medium heat. Add brown sugar and whisk until well incorporated. Add heavy cream and bring to a gentle boil. Once boiling (doesn't stop while stirred), stir and allow to boil 2 full minutes. Turn off heat and add vanilla and pinch of salt. Cool in a jar in the fridge and use for up to 3 weeks. It will thicken as it fully cools. This is a great dipping caramel or sauce for desserts like brownies, cheesecake and ice cream, or to sweeten drinks. ENJOY!