Place the sugar, salt, cream of tartar, and water in a deep, heavy- bottomed saucepan that holds at least 11/2quarts (the syrup will bubble up during cooking). Stir briefly to combine, then place over medium-high heat. From this point on, swirl the pan instead of stirring; this will help prevent crystals from forming.
When the mixture comes to a boil, reduce the heat to medium and watch carefully (no walking away!). The syrup will begin to turn golden at the edges; swirl the pan gently without lifting it off the heat to even out the color.
The syrup will continue to darken to light amber; as soon as you see any darker streaks, remove the pan from the heat and stir in the butter, a tablespoon at a time. Gradually add the heavy cream, stirring until it’s incorporated. Add the vanilla, stirring until the sauce is smooth.
Let the sauce cool for a few minutes before pouring into a heatproof container and storing; the sauce will thicken as it cools.
Store in the refrigerator; reheat briefly before serving.
Tips from our Bakers
- Why add cream of tartar to the sugar syrup? It's extra insurance against the syrup crystallizing. Many readers successfully make this sauce without it; but if you ever find yourself dealing with crystallized (instead of smooth) syrup, be sure to add the cream of tartar next time around.
- Don't let the sugar syrup become too dark before removing it from the heat; it'll continue to cook a bit even after it's off the heat. The darker the syrup the richer its flavor; but bitter/smoky notes start to creep in if you let it darken beyond medium amber.
Caramel is extremely versatile, making a good partner for a wide range of flavors. For salted caramel sauce, double the amount of salt in the recipe. Try flavoring the finished sauce with rum instead of vanilla, or simmer the cream in the recipe with herbs (rosemary, thyme, or lavender) or spices (chilies, star anise, juniper berries) before straining and adding to the recipe.
- For a twist, try Salted Rosemary Caramel Sauce. Place 3/4 cup sugar, 2 tablespoons boiled cider, 1/2 cup heavy cream, 2 tablespoons unsalted butter, 1/4 teaspoon salt, and one 4" sprig fresh rosemary in a medium saucepan. Bring to a boil, stirring once or twice at the beginning until the sugar dissolves. Once dissolved, cook over medium heat without stirring until the mixture reaches 230°F. Remove from the heat and strain into a heatproof container.
Looking for another delicious ice cream topping? See our recipe for Hot Fudge Sauce.