Pour the apple cider in a heavy bottom medium size pot and bring to boil. Reduce to a simmer, stirring every few minutes or so until reduced to about 1/4 cup and is thick and syrupy. This took about 45 minutes for us!
Remove from the heat and add the butter, cream, and sugars.
Place back over medium high heat and bring to a boil. Boil until the mixture reaches 252°F. Do not stir while it is boiling.
Remove from the heat and use a rubber spatula to mix in the cinnamon and salt, folding the caramel until it is smooth and creamy and no longer bubbling.
Pour the caramel into your prepared pan. Place in the fridge to set for about an hour.
Sprinkle with flaky sea salt and use a very sharp knife to cut into