
Heat the apple cider in a saucepan set over high heat until reduced to a 1/2 cup. Add the brown sugar and bring to a boil. Reduce the heat to medium high.
Heat the butter over medium heat, until just golden brown with a slightly nutty aroma (foam will subside and you'll see little brown flecks).
Whisk the sweetened condensed milk, vanilla and cinnamon together in a large bowl.
yields 1 1/2 quarts ice cream.