Preheat oven to 350F/177C. Line two, 8-inch cake pans with parchment paper; do not grease the sides. Prepare the chocolate sponge cake. Place the eggs, sugar and vanilla into a stand mixer bowl; whisk on high speed for 7 to 8 minutes, until the batter is thick and pale.
In a separate bowl, combine the flour, cocoa powder and salt. Sift the dry ingredients into the eggs in small batches, folding gently but thoroughly after each addition. Divide the batter evenly between the two cake pans. Bake in preheated oven for 18 to 20 minutes, until the tops are set. Remove the cakes from the oven, run a knife along the edge of the pan to release the cake. Cool the cake layers completely before using a serrated knife to split them in half.
Meanwhile, prepare the raspberry lemon curd; this can also be prepared ahead of time. Place the raspberries into a food processor and pulse into a puree. Strain the puree through a fine mesh sieve and discard any seeds.
In a small saucepan, combine the lemon juice, raspberry puree, sugar, salt, vanilla and eggs and egg yolks (save the egg whites for the meringue!). Whisk the ingredients together, then cook over medium heat, stirring constantly for 4 to 5 minutes. If any clumps form, strain the curd through a fine mesh sieve. Prepare the cornstarch slurry: mix the cornstarch and water together, then add to the curd. Cook for one more minute, then remove from heat.
Add the butter to the hot lemon curd and allow it to melt completely, then stir until well mixed. Cover the lemon curd with plastic wrap, making sure the wrap touches the surface of the curd, to prevent a film forming. Place the curd into the refrigerator (or freezer if you're in a pinch for time) and let it cool completely.
Once curd has cooled and thicken, assemble the cake. Split each chocolate layer in two, resulting in 4 cake layers. Spread a generous amount of the lemon curd onto each layer. For the last layer, add the curd to one side, then invert it onto the cake, leaving the top plain.
Prepare the meringue last. Place the egg whites into a stand mixer bowl and whisk just until soft peaks form. In a small saucepan, combine the water and sugar. Cook the mixture, not stirring, until it reaches 234F, soft ball stage. Once syrup is ready, set mixer to a medium speed and pour the syrup in a slow, steady stream. Once all the syrup is added, turn mixer up to high speed and whisk for 8 to 10 minutes, until a thick and glossy meringue forms. Add the vanilla last, then whisk for 30 more seconds.
Transfer the meringue into a pastry bag; I used Ateco tip #4FT. Pipe dollops of the meringue onto the cake. If desired, use a food torch to caramelize the meringue tips.
If not serving cake right away, keep it store in the refrigerator in a covered cake container to avoid drying.