1. In a small saucepan, combine sugar, salt, and the water. Cook over medium heat until sugar is a medium amber color (use strips of paper to test: the paler color is undercooked; the amber hue is just right), about 7 minutes; wash sides of pan with a pastry brush dipped in water to prevent crystals from forming. Remove from heat.

2. Stir in heavy cream; add butter, and stir until combined. Let cool to room temperature; stir in vanilla.