Prepare the Cake Base: Start by beating 5 egg whites with 50 g of sugar until you achieve stiff peaks. In a separate bowl, beat 5 egg yolks with another 50 g of sugar until creamy. Gradually fold in the sifted flour and carefully add the egg whites, combining gently using enveloping movements.

Bake the Cake: Pour the cake batter into a greased 30x40 cm tray and bake in a preheated oven at 210 degrees Celsius for about 11 minutes. The cake should spring back when lightly touched.

Make the Syrup: In a small saucepan, combine 100 g water, 100 g sugar, and a splash of rum. Bring to a boil and then remove from heat to cool.

Prepare the Cream Filling: In a saucepan, combine 300 g milk, 3 egg yolks, 30 g cornstarch, 65 g sugar, and a splash of vanilla paste. Heat gently while stirring until thickened, then mix in 100 g of melted milk chocolate until smooth.

Assemble the Cake: Once the cake is baked, brush it generously with the syrup. Spread a thin layer of the cream filling and cut the cake into three strips, each about 10 cm wide. Roll these strips carefully to create a vertical cake.

Make Swiss Meringue Cream: In another bowl, combine 80 g egg whites and 160 g sugar and heat gently, stirring constantly, until reaching 74 degrees Celsius. Remove from heat, beat until cool, and then incorporate 160 g butter one piece at a time before adding 120 g of melted dark chocolate. This should create a silky, luscious cream.

Finish the Cake: Cover your assembled vertical cake with the Swiss Meringue cream, smoothing it out for an elegant finish.