In a medium saucepan, combine raspberries, granulated sugar, lemon juice, lemon zest, and water. Bring to a boil over medium heat, then reduce to a simmer for 10-15 minutes, stirring occasionally.

Once the raspberries have broken down, strain the mixture through a fine sieve, mix in cornstarch slurry to thicken, and let cool before refrigerating.

Preheat your oven to 325°F (163°C) and grease two round cake pans, lining the bottoms with parchment paper.

In a mixing bowl, cream unsalted butter and sugar until light and fluffy. Add in pasteurized egg whites, mixing until well combined.

Incorporate cake flour, baking powder, and salt, alternating with sour cream and remaining water until a smooth batter forms.

Divide the batter evenly and bake for 40-42 minutes, or until a toothpick inserted into the center comes out clean.

While the cake layers are baking, prepare the simple syrup by combining equal parts water and granulated sugar in a small saucepan. Bring to a boil, stirring until sugar dissolves. Let cool to room temperature.

In a large mixing bowl, beat the softened unsalted butter with an electric mixer until creamy and smooth. Add in lemon juice, lemon zest, and salt, mixing until well incorporated.

Gradually sift in powdered sugar, alternating with heavy cream, until a fluffy consistency is achieved. Fold in melted white chocolate chips.

Once cake layers have cooled, remove them from pans. Brush tops of each layer with prepared simple syrup.

Layer one cake on a serving plate, followed by raspberry filling and a layer of white chocolate buttercream. Repeat with second layer and frost the entire outside with remaining buttercream.

Chill the assembled cake in the refrigerator for at least one hour to allow flavors to meld and frosting to set.

Decorate with additional raspberries or white chocolate shavings as desired before serving.