This sauce, which gets swirled into our Caramel Corn Ice Cream, is great as a sundae topping.
Stir together sugar and 1/2 cup water in a medium saucepan over medium-high heat. Bring to a boil, stirring constantly. When sugar has dissolved, raise heat to high. Cook, without stirring, until mixture is medium amber, 7 to 8 minutes.
Remove from heat. Carefully stir in cream (it will steam), then the vanilla and salt. Let cool 5 minutes. Whisk in butter.