How to Make It
Preheat oven to 350°F.Grease 4 (6-inch) cast-iron skillets evenly with 2 tablespoons of the butter. Set aside.
Place 2 cups of the cream in a saucepan. Bring to a simmer over medium, and remove from heat. Whisk together eggs and brown sugar in a large bowl. Slowly add warm cream in a steady stream, whisking constantly. Stir in vanilla extract. Add torn bread, making sure bread is completely submerged, and let mixture stand 10 minutes.
Meanwhile, cut each apple into about 30 thin slices; toss together apple slices, granulated sugar, and lemon juice in a large bowl.
Spoon 1/3 cup of the bread mixture into each buttered skillet, and press into an even layer. Top each with a layer of about 16 apple slices, and another 1/3 cup of the bread mixture. Arrange 16 to 18 apple slices in a concentric circle on top of bread mixture in each skillet.
Place remaining 4 tablespoons butter in a microwave-safe bowl, and microwave on HIGH until melted, about 15 seconds. Brush melted butter evenly over apples, and sprinkle evenly with 2 teaspoons of the cinnamon sugar. Place skillets on a rimmed baking sheet.
Bake in preheated oven until custard is cooked and apples are mostly tender, about 40 minutes.
Meanwhile, combine remaining 1 cup cream and 2 teaspoons cinnamon sugar in a small chilled bowl. Beat with an electric mixer on high speed until stiff peaks form, 2 to 3 minutes. Chill until ready to serve.
Remove skillets from oven, and let stand 10 minutes. Top each warm skillet with 2 tablespoons of the Caramel Sauce, and a large dollop of cinnamon cream.