Preheat oven to 350° F. Prepare the pans - I apply a generous amount of cake release using a pastry brush.
Melt butter in a large saucepan over medium-low heat; add cocoa, stirring until smooth. Whisk in the espresso water and remove from heat.
Add the sugar, sour cream, vanilla, and eggs to the warmed cocoa mixture and whisk until smooth.
In a medium bowl, combine the flour, baking soda, and salt. Add to the first mixture, whisking until well blended.
Pour batter into the prepared pans. Bake for 30-40 minutes, or until it feels firm to the touch and has slightly pulled away from the sides of the pan.
Cool in pans on a rack for 5 minutes. Remove from pan by placing the rack over the cake and invert, tapping pan lightly, if required to loosen.
While still warm, wrap in plastic wrap and place in the freezer to cool. I leave mine overnight. I find this seals in the moisture, flavour and make makes torting and working with the cakes more manageable.
To make the frosting:
Ensure all equipment is grease-free.
Fill a heavy duty pot about a quarter of the way with water and place on the stove over medium heat to simmer.
Add egg whites, sugar and salt to the mixing bowl and whisk together lightly with a hand whisk, just until combined. Attach a thermometer to the side of the bowl and place the bowl over the pot of simmering water, ensuring the bottom of the bowl is not in contact with the water in the pot. Whisk the sugar egg white mixture constantly, but gently, until temperature reaches 160°F.
Once at the correct temperature, remove carefully from heat, wipe the moisture away from the bottom of the bowl and transfer mixing bowl to the stand mixer. With the whisk attachment, begin to whip the meringue on high speed until it is thick, glossy, and the bottom of the bowl is no longer warm to the touch. Do not begin adding butter while the bowl is still warm.
Switch from your whisk to paddle attachment and with mixer on low speed, add butter cubes, one at a time, until incorporated. Continue to mix until it has reached a silky smooth texture.
Add crushed vanilla beans and vanilla extract, continuing to beat on low speed until well combined.
Assembly:
Remove cakes from freezer a few hours ahead of assembling, wrap in tea towels and allow to defrost at room temperature. Level cakes, once defrosted.
Using a cake board just slightly larger than the size of your cake, spread a small amount of frosting over the board and place the first layer on the board, centering it.
Attach a #12 plain round piping tip
to a bag and fill with frosting. Pipe a round dam just inside edge of the cake.
Generously coat the top of the cake with raspberry chocolate sauce. Place a handful of fresh, chopped raspberries over the sauce and the fill in with frosting.
Place a layer of cake on top of frosting and press lightly, but firmly until levelled. Repeat for the remaining layers. Use the frosting in the piping bag to fill in any gaps between layers and use an offset spatula to seal the seams.
Add a thin layer of frosting over the entire cake to seal in the crumbs and place in the fridge for 15-20 minutes.
Remove from the fridge and frost the cake, using the cake board as your guide for applying an even coat of frosting. Smooth out the frosting using a spatula. Refrigerate.
Let stand at room temperature for an hour before serving. Enjoy!