Begin by preheating your oven to 400°F (200°C). Melt 2–3 tbsp of butter in a frying pan over medium heat, then add 1½ cups of stale bread crumbs, stirring constantly for about 5 minutes until they become crisp and golden brown.
This toasting step is indispensable, as it transforms the bread crumbs into a crunchy, flavorful component that will form the structural layers of your dessert. Once the crumbs reach a rich golden color, remove the pan from the heat and set aside.
While the bread crumbs toast, prepare your apples by tossing 2 lb (1 kg) of thinly sliced tart apples with ½ cup of granulated sugar, 1 tbsp of lemon juice, and 1–2 tsp of ground cinnamon. This mixture should sit for a few minutes, allowing the apples to release their juices and absorb the warm spice flavors.
In your deep 2-quart (2-liter) ovenproof dish, press one-quarter of the crisp bread crumbs firmly over the bottom to create a base layer. Top this with half of the apple mixture, spreading it evenly, then sprinkle another quarter of the bread crumbs over the apples.
Layer the remaining apple mixture on top of the second layer of bread crumbs, pouring any accumulated juices from the bowl over the apples. Cover everything with the final quarter of the toasted bread crumbs and sprinkle lightly with additional granulated sugar for extra sweetness and crispness.
Cover the dish with foil and bake for 20 minutes, then remove the foil and continue baking for another 20 minutes until the apples are tender and the top is golden brown. Serve warm, allowing the layers to settle slightly before spooning into bowls.