In a glass microwave-safe bowl, melt 1 stick of butter (heat for 60 seconds).
Stir in brown sugar, corn syrup, boiled cider, sweetened condensed milk, cinnamon, and a pinch of salt.
Microwave for 8 minutes. Stir. Microwave an additional 60-90 seconds. Stir.Note: If you have a candy thermometer, the caramels are the perfect soft consistency at 245-248 degrees. You can also drop a small amount of caramel into a cup of ice water and if it sets up enough to be chewy and roll up into a soft ball it is done. I've made these enough that I know that they are done when cooked for 8 minutes and then an additional 90 seconds. Every microwave is different so it's better to err on the side of having slightly softer caramels vs. overheating them.
Pour caramel into the prepared baking dish. Let set up in the refrigerator for 30 minutes. Note: You can leave it in the refrigerator longer, but if the caramels get too cold they will be hard to get out of the pan. That's ok though, just let them sit on the counter until they come to room temperature and they'll be perfect again.
Remove caramels from dish by pulling up on the parchment paper.Slice into squares.