1. Preheat the oven to 350°F (175°C). Line a 9-inch (22 cm) springform pan with parchment paper and lightly grease the sides.

2. In a medium bowl, sift together flour, salt, and vanilla sugar. Set aside.

3. In a large bowl, beat eggs and sugar with an electric mixer on high speed until pale and fluffy, about 2 minutes. Melt white chocolate in a double boiler or microwave, stirring until smooth. Let cool slightly before folding into egg mixture.

4. Gently fold flour mixture into wet ingredients until just combined. Stir in lemon zest.

5. Pour batter into prepared pan and smooth the surface. Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.

6. Let cake cool in the pan for 10 minutes before releasing the sides. Transfer to a wire rack to cool completely.

7. Top cooled cake with fresh raspberries and a sprinkle of granulated sugar, if desired. Handle hot surfaces and sharp knives carefully to avoid accidents or injuries.