1. Preheat your oven to 350°F or 175°C. Line a baking sheet with parchment paper to prevent the walnuts from sticking.

2. Spread the walnut halves evenly on the prepared baking sheet and bake for 10-12 minutes, or until they are nicely caramelized and fragrant. Once done, set them aside to cool down.

3. In a medium-sized bowl, whisk together 240 ml or 1 cup of heavy cream, 15 ml or 1 tablespoon of lemon juice, and 15 g or 1 tablespoon of vanilla sugar until stiff peaks form. Be patient and whisk until the mixture becomes stiff and holds its shape.

4. In a separate bowl, mix together 200 g or 1 cup of granulated sugar and the grated zest of 1 lemon.

5. Gently fold the sugar mixture into the whipped cream until well combined. Make sure to fold the mixture gently to avoid deflating the whipped cream.

6. Spoon the creamy lemon mixture into individual serving cups or a large serving dish. Refrigerate for at least 2 hours or until chilled and set.

7. Just before serving, top the creamy lemon mixture with the caramelized walnuts and a sprinkle of sugar if desired. This will add a nice crunch and a touch of sweetness to the dish.