In a large mixing bowl, whisk together eggs, milk, sugar, cinnamon, and vanilla until well combined and the mixture is slightly frothy.
Arrange the slices of bread in a greased baking dish, overlapping slightly to fit as many as possible.
Pour the custard mixture evenly over the bread, ensuring all slices are soaked. Cover the dish with plastic wrap and refrigerate overnight to allow the bread to absorb the custard fully.
The next morning, preheat your oven to 375°F (190°C). Place the thinly sliced apples evenly over the soaked bread in the dish.
Sprinkle additional cinnamon over the top, if desired, and dot with melted butter for a crisp, caramelized crust.
Bake uncovered for about 40 minutes, or until the top is golden brown and the custard is set with a slight puff in the middle. The aroma of cinnamon and baked apples will fill your kitchen.
Remove from the oven and let it cool slightly before slicing. Optionally, sprinkle with cinnamon sugar for an extra crunchy topping.
Serve warm, spooning out portions that reveal the tender bread, caramelized apples, and crispy edges. Enjoy the comforting, aromatic bites!
