1. Prepare the Bread: Start by cutting your day-old bread into 1-inch cubes. Distribute these bread cubes evenly in a lightly greased 9×13-inch baking dish. Ensure the cubes are spread out so they can all absorb the custard.

2. Dice the Apples: Peel, core, and dice your apples into small, uniform pieces. Scatter these apple pieces over the bread cubes in the baking dish. This ensures a good distribution of apple in every bite.

3. Whisk the Custard: In a large bowl, whisk together the eggs, whole milk, heavy cream, brown sugar, ground cinnamon, vanilla extract, and salt until well combined and the sugar has dissolved. Make sure there are no streaks of egg white remaining.

4. Pour and Drizzle: Carefully pour the egg custard mixture evenly over the bread and apples in the baking dish. Gently press down on the bread with a spatula to ensure all the pieces are submerged and soaking up the liquid. Drizzle half of the caramel sauce (about 1/4 cup) over the top of the casserole.

5. Chill Overnight: Cover the baking dish tightly with plastic wrap and refrigerate for at least 8 hours, or preferably overnight. This crucial step allows the bread to fully absorb the custard, leading to a wonderfully tender and custardy texture when baked.

6. Bake in the Morning: The next morning, preheat your oven to 375 F (190 C). Remove the casserole from the refrigerator and let it sit at room temperature for about 15-20 minutes while the oven preheats. This helps it bake more evenly.

7. Cook to Golden Perfection: Bake the casserole, uncovered, for 45-55 minutes, or until it’s golden brown on top, puffed up, and the center is set (a knife inserted into the center should come out clean). If the top starts to brown too quickly, you can loosely tent it with aluminum foil.

8. Serve Warm: Let the casserole cool for a few minutes before serving. Drizzle with the remaining caramel sauce (warmed slightly, if desired) and any other desired toppings.