In a medium sauce pan, whisk together ½ cup heavy cream, brown sugar, butter, corn syrup, and salt. Whisking occasionally, bring the mixture to a boil over medium-high heat and cook until it reaches 250°F according to the candy thermometer (about 5-10 minutes).

Whisk in the remaining ½ cup heavy cream and the vanilla extract. Bring the mixture back to a low boil and whisk vigorously for about a minute. Remove the mixture from heat, transfer to a heat-safe bottle or jar, and store in the fridge until use.