01 - Preheat oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.
02 - In a large skillet over medium heat, melt 2 tablespoons butter. Add diced apples, 2 tablespoons brown sugar, and 1/2 teaspoon cinnamon; cook, stirring, for 5 to 7 minutes until apples are tender. Remove from heat.
03 - In a large mixing bowl, whisk together eggs, whole milk, heavy cream, granulated sugar, vanilla extract, ground cinnamon, ground nutmeg, and salt until well combined.
04 - Spread cubed bread evenly into the prepared baking dish. Distribute the cooked apples over the bread.
05 - Pour the custard mixture evenly over the bread and apples. Gently press down with a spatula to help the bread soak up the liquid.
06 - In a small saucepan, melt 1/2 cup unsalted butter over medium heat. Stir in 3/4 cup brown sugar and a pinch of salt; cook for 2 to 3 minutes, stirring until smooth. Remove from heat and whisk in 1/4 cup heavy cream until fully blended.
07 - Drizzle the caramel sauce evenly over the entire casserole.
08 - Transfer to oven and bake uncovered for 40 to 45 minutes, or until golden brown and set in the center.
09 - Allow to cool for 10 minutes before slicing. Serve warm; optionally top with extra caramel sauce or powdered sugar.