1. Preheat your oven to 350°F (180°C) and line three 8-inch cake pans with parchment paper.
2. Melt 8 ounces of chopped white chocolate in ¾ cup of whole milk over low heat, stirring until smooth. Let it cool.
3. In a bowl, mix 2 ½ cups of all-purpose flour, 2 ½ teaspoons of baking powder, and ½ teaspoon of salt.
4. In a separate bowl, cream ¾ cup unsalted butter with 1 ¾ cups granulated sugar until light and fluffy.
5. Gradually add 5 egg whites to the butter mixture, beating well after each addition.
6. Incorporate 1 teaspoon of vanilla extract and the cooled white chocolate mixture into the egg and butter mixture.
7. Slowly add the dry ingredients to the wet ingredients, mixing until just combined without overmixing.
8. Divide the batter evenly among the prepared cake pans and bake for 24-28 minutes or until a toothpick inserted in the center comes out clean.
9. Allow the cake layers to cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.
10. To prepare the white chocolate ganache, place 12 ounces of chopped white chocolate in a heatproof bowl.
11. Heat ¾ cup of heavy whipping cream until it begins to simmer, then pour it over the chopped white chocolate.
12. Allow the mixture to sit for a few minutes to melt the chocolate, then stir until smooth.
13. Stir in 1 teaspoon of vanilla extract and let the ganache cool before using it as a frosting.
14. To make the raspberry filling, combine 12 ounces of fresh or frozen raspberries, ¾ cup granulated sugar, 1 tablespoon cornstarch, 1 tablespoon lemon juice, and 1 teaspoon lemon zest in a saucepan.
15. Cook the raspberry mixture over medium heat, stirring continuously until it thickens. Optionally, strain the filling to remove seeds for a smoother texture and let it cool.
16. Spread a thin layer of white chocolate ganache on one of the cake layers.
17. Add a layer of raspberry filling on top of the ganache and carefully place the second cake layer on top.
18. Repeat the process with the second layer, topping it with ganache and raspberry filling before placing the third cake layer.
19. Frost the entire cake with the remaining ganache, smoothing it evenly over the top and sides of the cake.
20. Decorate the cake with fresh raspberries and white chocolate shavings for garnish.
21. Chill the assembled cake in the refrigerator for at least an hour to allow the ganache to set before serving.
22. Slice the cake and serve with extra raspberry sauce or fresh raspberries if desired. Enjoy your luxurious White Chocolate Raspberry Cake!