01 - Preheat oven to 350°F. Generously grease a 9x13-inch baking dish.
02 - Melt 2 tablespoons unsalted butter in a large skillet over medium heat. Add diced apples, 2 tablespoons brown sugar, and 1/2 teaspoon ground cinnamon. Sauté for 5–7 minutes until apples become tender, stirring occasionally. Remove from heat.
03 - In a large mixing bowl, thoroughly whisk together eggs, whole milk, heavy cream, granulated sugar, vanilla extract, ground cinnamon, ground nutmeg, and salt until smooth and fully incorporated.
04 - Arrange cubed bread evenly in the prepared baking dish. Evenly distribute the cooked apples over the bread layer.
05 - Pour egg mixture evenly over the bread and apples. Lightly press down so the bread absorbs the liquid.
06 - In a small saucepan over medium heat, melt 1/2 cup butter. Stir in 3/4 cup brown sugar and a pinch of salt; cook for 2–3 minutes, stirring constantly. Remove from heat and whisk in 1/4 cup heavy cream until smooth.
07 - Drizzle prepared caramel sauce evenly over the assembled casserole.
08 - Transfer dish to the oven and bake uncovered for 40–45 minutes, until golden brown and custard is set in the center.
09 - Allow to cool for 10 minutes before slicing. Optionally, finish with extra caramel or a light dusting of powdered sugar prior to serving.