Combine the sugar and cider in a medium sauce pan (big enough to allow for some serious bubbling down the line) over medium low heat.
Swirl occasionally to combine the sugar and help it dissolve. Once the sugar has completely dissolved and the mixture has begun to simmer put in the candy thermometer and go about your business.
Every couple of minutes swirl but don’t stir.
Once the sugar cider mixture has reached 240 degrees (a degree or two higher is ok but not lower)- about fifteen minutes- remove from heat and add the butter and the cream, stir (yes you can stir now, and yes, this is when the mad bubbles might happen but don’t be sad if they don’t) to combine and then stir in the vanilla.
Allow to cool before tasting.
Store, refrigerated, in a half pint jar for weeks.
Spiced Apple Caramel Sauce https://www.recipefiction.com/2014/12/spiced-apple-caramel-sauce.html