2cupsapple cider(or 1/4 cup boiled cider) not apple juice
To make the boiled cider:
Pour the apple cider into a large, heavy-bottom deep saucepan. Cook over medium-high heat and bring cider to a boil. Keep an eye on the cider to make sure it doesn’t boil over. The apple cider bubbles up quickly but will settle down after about 5 minutes of simmering. Boil until the cider is reduced to 1/4 cup. Don’t let it get too thick or syrupy. Remove from the heat and set aside. Use immediately or refrigerate until needed.
To make the caramel sauce:
Pour the cream, salt, apple cider. cinnamon and nutmeg into a small heavy-bottom saucepan. Warm over medium-low heat while preparing the syrup mixture.
Pour 1 cup of water into a 2-quart heavy-bottomed saucepan. Pour the sugar into the center of the pot taking care to keep the granules away from the sides of the saucepan.
Cover the pan and bring the mixture to a boil over high heat. Uncover and insert a candy thermometer and continue to boil until the mixture is thick, light golden brown in color, and registers 300 degrees F. This will take about 10-15 minutes.
Reduce the heat to medium and continue cooking until the sugar is deep amber in color, almost begins to smoke and registers 350 degrees F on the thermometer; about 5 minutes.
While the syrup reaches the desired temperature, turn up the heat under the cream until it starts to simmer. If the cream simmers before the syrup reaches 350 degrees F, remove it from the heat and set aside.
Once the syrup reaches 350 degrees F, remove from the heat. Add one-fourth of the hot cream to the sugar mixture. The mixture will bubble and spit. Allow the mixture to settle down then add the remaining cream. Once the bubbling subsides, gently whisk until smooth. Add the butter and whisk until combined.
Transfer the caramel sauce to a heat-safe container, allow it to cool until just warm and serve. Caramel sauce can be covered and refrigerated for up to 1 month. Reheat gently in the microwave on 50% power until heated through.