Preheat your oven to 350°F (175°C). Grease a baking dish with a teaspoon of butter to prevent sticking.
In a large mixing bowl, whisk together eggs, milk, vanilla extract, ground cinnamon, and brown sugar until smooth and well combined. The mixture should be slightly frothy and fragrant with cinnamon.
Add the sliced bread cubes into the custard mixture, gently folding to coat all the bread evenly. Let it soak for about 5 minutes so the bread absorbs the custard.
Meanwhile, toss the sliced apples with a tablespoon of melted butter and a teaspoon of cinnamon, coating them evenly. Spread the apples in the bottom of the prepared baking dish, creating a single layer.
Pour the soaked bread mixture gently over the layer of apples, spreading evenly to cover all the fruit. The bread should nestle among the apple slices.
Sprinkle the remaining brown sugar over the top and dot with small pieces of the remaining butter for a caramelized topping during baking.
Bake in the preheated oven for 35 to 40 minutes, until the top is golden brown, the custard is set, and the apples are bubbly and tender.
Remove from the oven and let the bake rest for a few minutes. Drizzle with extra melted butter or serve warm, enjoying the aroma of cinnamon and baked apples.