01 -
In a heavy-bottomed medium saucepan over medium heat, mix brown sugar and butter, whisking continuously until the sugar dissolves and butter is completely emulsified. Keep whisking until thick and fully combined, about 3-4 minutes.
02 -
Slowly whisk in the cream (careful, it may hiss and bubble). Increase heat to medium-high until boiling, then reduce to medium-low and whisk constantly for about 5 minutes until thickened. Lower heat if it starts boiling again.
03 -
Remove from heat, stir in salt and vanilla. Let cool, whisking occasionally. The caramel will continue to thicken as it cools.