Heat milk and chocolate until melted and combined, cool to room temperature.*
Preheat oven to 350F. Grease and flour three 8" cake rounds and line with parchment.
In a medium bowl, whisk flour, baking powder, and salt until well combined. Set aside.
Using a stand mixer fitted with a paddle attachment, cream butter and sugar on med-high until pale and fluffy (approx 3mins). Reduce speed and add eggs one at a time fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and milk mixture, beginning and ending with flour (4 additions of flour and 3 of milk). Fully incorporating after each addition.
Bake for approx. 40mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack and cool completely.
White Chocolate Swiss Meringue Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.**
Place bowl over a double boiler on the stove and whisk constantly until the mixture is hot and no longer grainy to the touch (approx. 3mins). Or registers 160F on a candy thermometer.
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.***
Add white chocolate and whip until smooth.
Reserve 1/3rd of the prettiest raspberries (160g) for the top of the cake. Very roughly chop remaining 2/3rds of the raspberries (330g). I basically just made sure each was cut in half.
Place one layer of cake on a cake stand or serving plate. Spread approx. 3 Tbsp of raspberry jam evenly across the layer, right to the edges. Top with 1 cup of buttercream and spread evenly. Press half of the chopped raspberries evenly into the frosting. Repeat with next layer.
Top with final layer of cake and crumb coat. Add 1 cup of buttercream to the very top and smooth until it hangs over the sides. Use an icing smoother to smooth the sides and create a lip on the top with the frosting.
Dollop a bit of frosting on the top and spread out in a rustic manner. Top with fresh raspberries and thyme sprigs if desired.
* You can do this in the microwave, stirring between 30 second bursts or in a pot in the stove, stirring constantly, or in a double boiler, stirring occasionally. ** Wipe your mixer bowl and whisk down with lemon juice or vinegar to make sure it is completely grease free and make sure there is no trace of yolk in your whites or your meringue will not stiffen. *** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth. If it looks soupy, place it in the fridge for 20mins and rewhip.