In a sauce pan over medium heat, melt butter. Continue to cook butter, stirring frequently and adjusting temperature as needed, to allow butter to get brown bits on the bottom. Cook until butter becomes a golden brown color and smells nutty, about 2-3 minutes. Add brown sugar and whisk until sugar has dissolved, being careful not to burn. Reduce heat to low and add heavy whipping cream, whisking quickly until well combined. Simmering an additional 1-2 minutes or so until thickened to more of a thick syrupy consistency. Remove from heat and add vanilla and sea salt stirring to combine. Let cool until warm but no longer hot, then transfer to a large glass jar for storage. Keep refrigerated. Mixture will become thicker as it cools, but can be heated in the microwave briefly to return to a pourable consistency.
Recipe by Wright Family Table at https://www.wrightfamilytable.com/brown-sugar-caramel-sauce/