Stir together sugar, salt, and the water in a small saucepan. Cook over medium heat until mixture turns medium amber, washing down sides of pan with a wet pastry brush to prevent crystals from forming.Advertisement
Remove from heat; carefully stir in cream (caramel will steam). Add butter; stir until combined. Let cool to room temperature; stir in vanilla. If not using immediately, refrigerate in an airtight container up to 2 weeks. Reheat, and let cool to room temperature before serving.