Bring the cup of cider to a vigorous boil in a havy bottomed small sauce pan. Cook until reduced by at least half, maybe two-thrids, depending on how thick you like your syrup. Remove from heat. Note: You can use right away or make ahead of time and store in a container in the fridge.

Heat your oven to 425. Heat your cast iron skillet over medium heat and melt two tablespoons of the butter and the brown sugar together. Add your apple slices and gently cook until the apple are slightly sofetened, I'd say five minutes tops. Remove the apples from the skillet and wipe it out - DO NOT WASH - with a paper towel. Add the last two tablespoons of butter to the skillet and melt and swirl around the bottom of the pan and up the sides.

While the apples are cooking, whisk together the flour, milk, eggs, sugar, salt and cinnamon until smooth. You want a nice thin batter, almost like crepe batter. Make sure to do this while the apples are cooking, and not after. You want a solidly hot cast iron skillet when you pour this into it.

Put the apple back into the pan, in the center and pour the batter over and around the apples. Immediately put in the oven - middle rack if you can. bake this about 15 minutes. Check after 12 minutes, it should be puffing up around the edges and browned, but the center should still look like a custard with apples. Always takes15 minutes for me.

Remove from oven and drizzle with that glorious cider caramel syrup. Slice up and enjoy!