01 -
In a medium heavy-bottomed saucepan, melt the unsalted butter over medium heat.
02 -
Add the dark brown sugar, large-flake sea salt, and heavy cream to the melted butter. Stir thoroughly with a rubber spatula until the mixture is well blended. Bring to a gentle boil, scraping down the sides of the pan as needed, and let it boil for 4 to 5 minutes.
03 -
Remove the saucepan from the heat and stir in the vanilla extract. Pour the sauce into a heatproof container and allow it to cool before serving.