First reduce the cider: in a small pot boil the cider on high for 30-45 minutes until it has been reduced to about ¼ of a cup.
Once the caramel has reduced, add the butter, sugar, salt and cinnamon then stir and let it come to a boil.
Once the temperature reaches 245 turn off the heat and add the milk and heavy cream.
Some of the caramel might harden and float to the top, return to heat and whisk it as it warms and it will melt into the milk.
Add the vanilla and whisk then set it aside to come to room temperature.
Set it in an airtight container and in the fridge to chill overnight.
The next day, stick the container you plan to store it in in the freezer to chill so it is cold before you add the ice cream. Whisk your base together (it tends to set a bit at the top) and freeze according to your machine’s instructions. Store in the freezer in an airtight container.