Cook sugar in a 3-qt. heavy saucepan over medium heat 6 to 8 minutes or until sugar caramelizes, tilting and swirling pan to incorporate mixture. Stir in whipping cream. (Mixture will bubble and harden.) Cook, stirring constantly, until mixture melts and begins to boil (about 5 minutes). Quickly pour sauce into a bowl; stir in vanilla, and salt. Let cool 15 minutes. Serve warm or cool.
Note: To make ahead, cover and chill up to 3 weeks. To reheat, cook, uncovered, in a microwave-safe glass bowl at MEDIUM LOW (30% power) for 2 minutes or until warm, stirring once.
If you detect a whiff of something bitter after caramelizing the sugar, you might have burned the sugar and need to start over.