Add the frozen raspberries, granulated sugar, and lemon juice into a 3-quart saucepot over medium heat, bring to a boil, and cook for 3-4 minutes stirring often to ensure the raspberries do not burn.

Whisk together the cornstarch and water in a small bowl until the cornstarch is fully dissolved. While whisking constantly, add the cornstarch slurry to the raspberries.

Cook the raspberries for an additional 1-2 minutes or until the mixture starts to thicken up. Remove from the heat and allow the raspberry filling to cool completely before adding to the cake layers. The filling will thicken as it cools. Once the raspberries have cooled down, transfer them to a bowl and cover them with plastic wrap. Refrigerate the raspberry filling for 2 hours or until ready to add to the cake. Be sure that your filling is completely cool before adding to your cake layers.

Preheat oven to 350°F. Spray 3 (8-inch round) cake pans with baker’s spray. Set aside.

Add the boxed white cake mix, white chocolate instant pudding mix, liquid egg whites, whole milk, canola oil, and clear vanilla flavoring in a large mixing bowl. Beat with a handheld mixer on medium speed for 2 minutes or until no lumps remain.

Evenly divide the batter between the prepared cake pans and spread it into an even layer using a small offset spatula. This will be a thick batter. You can use a kitchen scale to weigh the pans to ensure you have evenly divided the batter. Each pan should get approximately 1 cup of batter. Bake for 18-20 minutes or until a toothpick inserted in the center of the cake comes out clean.

Allow the cake to cool in the pans for 10 minutes before transferring them to a wire rack to cool completely before adding the raspberry filling and frosting.

In a microwave-safe bowl, melt the chopped white chocolate baking bar for 1-2 minutes, in 30-second intervals, whisking between each interval until smooth. Set aside and allow to cool.

In the bowl of a stand mixer fitted with the paddle attachment, on medium-high speed, add the unsalted butter and salt. Beat for 1-2 minutes or until light and fluffy.

Add the powdered sugar, one cup at a time, and beat until all the powdered sugar has been incorporated. You will need to start the mixer on low and build up the speed to avoid getting powdered sugar all over your counter. You will need to stop and scrape down the sides and bottom of the bowl between additions to ensure your frosting is evenly mixed.

With the mixer on medium speed, slowly add the cooled melted white chocolate until fully mixed into the butter. Add the heavy cream and clear vanilla flavoring to the frosting and mix for an additional 2-3 minutes or until the frosting is smooth and fluffy.

Remove 1½ cups of the frosting from the bowl and add it to a piping bag fitted with a piping tip or a large zip-top bag with the corner snipped off. This is to be used for the garnish and piping around the edge of each layer to keep the raspberry filling from bleeding into the cake's frosting.

If your cake layers are slightly domed in the center, you can use a large serrated knife to create a level cake layer. Place one of the cake layers onto a large plate or cake stand. Spread a thin layer of the white chocolate frosting onto the cake layer, then with the reserved frosting in the piping bag, pipe a thin circle around the outer edge of the cake. Spread half of the chilled raspberry filling over the frosted cake layer, keeping it inside the piped circle around the edge of the cake. Place the cake into the freezer for 10-15 minutes, then remove from the freezer and repeat for the second cake layer. Freeze the cake again for another 10-15 minutes before adding the final cake layer.

Place the third cake layer onto the top and add the remaining white chocolate frosting to the top and sides of the cake, being sure to smooth the frosting out as evenly as possible.

With the remaining frosting in the piping bag, pipe a decorative border around the outer edge of the top of the cake, add a circle of fresh raspberries around the inside of the piped frosting, followed by an addition of white chocolate shavings to the center of the top of the cake.