Prepare the Cake Layers:

1. Preheat and prep: Preheat your oven to 350°F (175°C). Grease three 8-inch round cake pans, line the bottoms with parchment paper circles, and grease the parchment. Lightly flour the pans and tap out excess.
2. Melt white chocolate: Melt the 6 oz white chocolate in a double boiler or microwave (30-second intervals, stirring between). Let cool to lukewarm.
3. Mix dry ingredients: In a medium bowl, whisk together cake flour, baking powder, baking soda, and salt. Set aside.
4. Cream butter and sugar: In a large bowl using an electric mixer, beat the butter and sugar on medium-high speed for 3-4 minutes until light and fluffy, scraping down the bowl as needed.
5. Add eggs: Add eggs one at a time, beating well after each addition. Mix in the vanilla extract and cooled melted white chocolate until combined.
6. Alternate wet and dry: With the mixer on low speed, add the flour mixture in three additions alternating with the buttermilk mixture (buttermilk plus oil) in two additions, beginning and ending with flour. Mix each addition just until incorporated. Don’t overmix.
7. Fold in berries: Toss the raspberries gently with 2 tablespoons all-purpose flour. Gently fold the floured raspberries into the batter using a rubber spatula, being careful not to crush them.
8. Divide and bake: Divide the batter evenly among the three prepared pans (about 2½ cups each). Gently smooth the tops. Bake for 28-32 minutes, until a toothpick inserted in the center comes out clean or with a few moist crumbs. The tops should spring back when lightly pressed.
9. Cool: Let the cakes cool in the pans on wire racks for 10 minutes. Then run a knife around the edges, invert onto the racks, peel off parchment, and cool completely before frosting (at least 1 hour).

Make the White Chocolate Buttercream:

10. Melt chocolate: Melt the 12 oz white chocolate and let it cool to lukewarm (if it’s too hot, it will melt the butter).
11. Beat butter: In a large bowl with an electric mixer, beat the room temperature butter on medium speed for 2-3 minutes until creamy and smooth.
12. Add melted chocolate: Add the cooled melted white chocolate to the butter and beat until combined and smooth.
13. Add sugar gradually: With the mixer on low, gradually add the sifted powdered sugar, 1 cup at a time, beating well after each addition.
14. Add flavorings: Mix in vanilla extract and a pinch of salt.
15. Adjust consistency: Add heavy cream 1 tablespoon at a time until the frosting reaches a smooth, spreadable consistency. Beat on medium-high for 1-2 minutes until light and fluffy.

Assemble the Cake:

16. Level layers: If your cake layers have domed tops, use a serrated knife to level them for easier stacking.
17. First layer: Place one cake layer on a cake board or serving plate. Spread about 1 cup of buttercream evenly over the top. Arrange a few fresh raspberries on the frosting if desired.
18. Second layer: Place the second cake layer on top. Spread another 1 cup of buttercream over it, adding more raspberries if desired.
19. Third layer: Place the final cake layer on top, flat side up for a smooth surface.
20. Crumb coat: Apply a thin layer of buttercream all over the cake (top and sides) to seal in crumbs. This is your crumb coat. Refrigerate for 20-30 minutes until the frosting is firm.
21. Final frosting: Apply the remaining buttercream in a thicker, final layer, smoothing with an offset spatula. Use a cake turntable if you have one, spinning while you hold the spatula still against the cake.
22. Decorate: Arrange fresh raspberries on top of the cake. Add white chocolate curls or shavings if desired. Dust lightly with powdered sugar just before serving.
23. Chill and serve: Refrigerate the cake for at least 30 minutes to set the frosting. Remove from the refrigerator 30 minutes before serving for best texture and flavor. Slice with a sharp knife, wiping it clean between cuts.