Arrange bread cubes evenly in the prepared baking dish.
In a large bowl, whisk together eggs, milk, heavy cream, granulated sugar, cinnamon, nutmeg, vanilla extract, and salt until well combined.
Pour the egg mixture evenly over the bread cubes, ensuring all pieces are moistened. Press down gently.
Cover the dish and refrigerate for at least 4 hours, or preferably overnight.
In a skillet, melt butter over medium heat. Add sliced apples, brown sugar, and lemon juice. Cook, stirring occasionally, until apples are tender, about 8-10 minutes.
Spread the sautéed apples evenly over the soaked bread mixture in the baking dish.
Preheat your oven to 350°F (175°C).
Bake the casserole uncovered for 45-55 minutes, or until the top is golden brown and the center is set.
Let stand for 10 minutes before serving.
Serve warm with your favorite toppings.
Notes
For a crispier topping, you can sprinkle streusel over the casserole before baking.
Challah or brioche bread works best due to its rich, eggy texture.
Ensure the bread is stale or slightly dried out for better absorption of the custard.
This casserole can be assembled the day before and baked in the morning.