Preheat your oven to 350°F (175°C). Grease and flour three 8-inch round cake pans. Line the bottoms with parchment paper.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the softened butter and granulated sugar on medium-high speed until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, beating well after each addition. Scrape down the sides and bottom of the bowl as needed. Beat in the vanilla extract.

Reduce the mixer speed to low. Add the dry ingredients in three additions, alternating with the buttermilk in two additions, beginning and ending with the dry ingredients. Mix until just combined – do not overmix.

Gently fold in the melted and cooled white chocolate with a spatula until evenly incorporated.

Divide the batter evenly among the three prepared cake pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean. Let the cakes cool in the pans for 15 minutes before inverting them onto a wire rack to cool completely.

In a small bowl, whisk together the cornstarch and cold water to create a slurry. Set aside.

In a small saucepan over medium heat, combine the raspberries, sugar, and lemon juice. Cook, stirring occasionally, until the raspberries break down and the mixture begins to simmer, about 5-7 minutes.

Whisk the cornstarch slurry into the simmering raspberry mixture. Continue to cook, stirring constantly, until the filling thickens, about 1-2 minutes. Remove from heat and transfer to a heatproof bowl. Let it cool completely to room temperature. You can place it in the fridge to speed this up.

In the bowl of a stand mixer with the paddle attachment, beat the softened butter on medium-high speed until creamy and pale, about 3 minutes.

Reduce the speed to low and gradually add the sifted powdered sugar, one cup at a time, mixing until incorporated. Add the salt.

Increase the speed to medium-high and beat for another 3-4 minutes until very smooth. Add the vanilla and heavy cream, and mix to combine.

With the mixer on low, pour in the cooled melted white chocolate. Once incorporated, increase the speed to medium-high and beat for 2 more minutes until light and fluffy. Do not overbeat once the chocolate is in, as it can cause it to separate.

Once the cake layers are completely cool, level the tops with a serrated knife if needed for flat, even layers.

Place one cake layer on your serving plate or cake stand. Pipe a dam of buttercream around the outer edge of the cake layer. This will hold the filling in.

Spread half of the cooled raspberry filling evenly inside the buttercream dam.

Place the second cake layer on top. Repeat the process: pipe a buttercream dam and spread the remaining raspberry filling.

Place the third cake layer on top. Apply a thin layer of buttercream over the top and sides of the entire cake to create a 'crumb coat'. Chill the cake in the refrigerator for at least 30 minutes to set the crumb coat.

Once chilled, apply the final, thicker layer of white chocolate buttercream over the entire cake, using an offset spatula or bench scraper for a smooth finish.

Decorate the top with fresh raspberries and white chocolate shavings. Chill the cake for at least 1 hour before slicing and serving to allow the frosting to set.