Preheat your oven to 375°F (190°C) and generously grease a baking dish with melted butter.
Arrange the slices of bread evenly in the baking dish, overlapping slightly if needed to cover the bottom.
Sprinkle the sliced apples evenly over the bread, distributing them across the entire surface for balanced flavor and appearance.
In a mixing bowl, whisk together the eggs, milk, sugar, cinnamon, and salt until well combined and slightly frothy.
Pour the custard evenly over the bread and apples, letting it soak in for a few minutes so the bread absorbs the mixture and turns soft.
Once the custard is absorbed, sprinkle the brown sugar evenly over the top for a sweet, caramelized crust.
Bake in the preheated oven for about 40 minutes, or until the top is golden brown and crispy, and the custard is set around the edges.
Remove from the oven and let it cool slightly before serving. The bake should be bubbly around the edges with a crispy, caramelized topping.