1. Prepare the Apples:

• Start by preheating your oven to 375°F (190°C).

• Peel, core, and dice the apples into small pieces. In a medium saucepan, melt 1 tbsp butter over medium heat and sauté the apples for about 5-7 minutes, until they become soft. Add 1 tbsp sugar and cinnamon (if using) to enhance the flavor. Continue to cook for another 2 minutes to allow the apples to caramelize slightly. Set the sautéed apples aside to cool.

2. Prepare the Soufflé Dish:

• Butter a soufflé dish (around 4 cups capacity) and sprinkle a little sugar inside. Swirl the dish to coat the base and sides with sugar. This process helps the soufflé rise evenly and gives it a delicate, sugary crust when it bakes.

3. Make the Soufflé Base:

• In a medium saucepan, heat the milk or cream over medium heat until it’s warm (but not boiling).

• In a separate bowl, whisk together the egg yolks, 1/4 cup sugar, and vanilla extract until smooth and slightly thickened. Gradually whisk in the warm milk or cream until everything is well combined. Pour this mixture back into the saucepan and cook over low heat, stirring constantly. The custard should thicken in about 3-5 minutes. Remove from heat and fold in the sautéed apples.

4. Whisk the Egg Whites:

• In a clean bowl, add the egg whites and a pinch of salt. Using an electric mixer or a whisk, beat the egg whites until stiff peaks form. This is crucial to achieving the soufflé’s signature puffiness.

5. Combine the Mixtures:

• Gently fold the beaten egg whites into the apple mixture, being careful not to deflate the air in the egg whites. The key here is to maintain the light, airy texture of the soufflé.

6. Bake the Soufflé:

• Pour the soufflé mixture into the prepared dish and smooth the top with a spatula. Place the dish in the preheated oven and bake for 20-25 minutes, or until the soufflé has risen and the top is golden brown. The soufflé should puff up beautifully in the oven.

7. Prepare the Hazelnut Topping:

• While the soufflé is baking, melt 1 tbsp butter in a small pan over medium heat. Add the finely chopped hazelnuts and toast them for 2-3 minutes, until they become fragrant and lightly golden. Add 1 tbsp sugar (or maple syrup if you prefer a more natural sweetener) and stir for another minute to combine. Set the topping aside.

8. Serve:

• Once the soufflé is done, remove it from the oven and let it rest for a minute or two. Then, sprinkle the toasted hazelnut topping on top of the soufflé. Serve immediately while it’s still puffed up and warm.