Warm milk and chocolate until melted and combined, then let it cool to room temperature.

Preheat oven to 350°F. Grease and flour three 8" cake pans, and line them with parchment paper.

In a medium bowl, whisk together flour, baking powder, and salt until well combined. Set aside.

Using a stand mixer with a paddle attachment, cream butter and sugar on medium-high until pale and fluffy (about 3 minutes). Reduce speed and add eggs one at a time, ensuring each is fully incorporated before adding the next. Mix in vanilla extract.

Alternate adding the flour mixture and milk mixture to the butter mixture, beginning and ending with flour. Fully incorporate each addition before adding the next.

Bake for about 40 minutes, or until a toothpick inserted into the center comes out mostly clean. Let cakes cool on a wire rack for 10 minutes before turning them out to cool completely.

Combine egg whites and sugar in the bowl of a stand mixer.

Place the bowl over a double boiler, whisking constantly until the mixture is hot and no longer grainy to the touch (about 3 minutes), or until it registers 160°F on a candy thermometer.

Attach the bowl to the stand mixer and whisk on medium-high until the meringue is stiff and cooled (the bowl should no longer be warm to the touch, about 5-10 minutes).

Switch to the paddle attachment. Slowly add cubed butter, mixing until smooth. Then add white chocolate and whip until smooth.

Set aside 1/3 of the prettiest raspberries (about 160g) for the top of the cake. Roughly chop the remaining raspberries (about 330g).

Place one cake layer on a cake stand or serving plate. Spread about 3 Tbsp of raspberry jam evenly over the layer. Top with 1 cup of buttercream, spreading it evenly. Press half of the chopped raspberries into the frosting. Repeat with the next layer.

Add the final cake layer and apply a crumb coat. Spread 1 cup of buttercream over the top, allowing it to hang over the sides. Use an icing smoother to smooth the sides and create a lip on the top with the frosting.

Dollop some frosting on the top and spread it out in a rustic manner. Top with fresh raspberries and thyme sprigs if desired.