Do not stir while cooking — swirl the pan only. Target deep amber color — not pale gold, not dark brown. Warm the cream before adding — cold cream can seize the caramel. Add butter while hot so it emulsifies. Vanilla and salt go in last off heat. If caramel seizes when cream is added, return to low heat and stir gently until smooth. Thickens when cold — warm briefly before using. Keeps 2 weeks refrigerated.