Divide the oven into thirds by positioning a rack in the upper third of the oven and the lower third of the oven.
Preheat the oven to 425◦F. (220◦C).
Line two 12½ x 15½- inch (31 x 39-cm) jelly-roll pans with parchment paper and brush with melted butter.
In the bowl of a stand mixer fitted with the whisk attachment (or using a handheld mixer), beat the egg whites until they form soft peaks. Add the granulated sugar and beat until the peaks are stiff and glossy. If you do not have another mixer bowl, gently scrape the meringue into another bowl and set aside.
In another bowl beat the eggs, sugar and almonds on medium speed until light and voluminous, about 3 minutes. Add the flour and beat on low speed until the flour is just combined (be very careful not to over mix here!).
Using a rubber spatula, gently fold the meringue into the almond mixture and then fold in the melted butter. Divide the batter between the pans and spread it evenly to cover the entire surface of each pan.
Bake the cake layers until they are lightly browned and just springy to the touch. This could take anywhere from 5 to 9 minutes depending on your oven. Place one jelly-roll pan in the middle of the oven and the second jelly-roll pan in the bottom third of the oven.
Put the pans on a heatproof counter and run a sharp knife along the edges of the cake to loosen it from the pan. Cover each with a sheet of parchment or wax paper, turn the pans over, and unmold.
Carefully peel away the parchment, then turn the parchment over and use it to cover the cakes. Let the cakes cool to room temperature.
For the soaking syrup:
½ cup (125 grams) water ⅓ cup (65 grams) granulated sugar 1 to 2 tbsp. of the flavoring of your choice (i.e., vanilla extract, almond extract, cognac, Limon cello, coconut cream, honey etc.) I used lemon.
Stir all the syrup ingredients together in the saucepan and bring to a boil. Remove from the heat and let cool to room temperature.
For the butter cream :
cup (100 grams) granulated sugar ¼ cup (60 grams) water.
seeds of one vanilla bean (split a vanilla bean down the middle and scrape out the seeds) or 1 tbsp. pure vanilla extract 1 large egg 1 large egg yolk 1¾ sticks (7 ounces; 200 grams) unsalted butter, at room temperature .
flavouring of your choice (a tablespoon of an extract, a few tablespoons of melted white chocolate, citrus zest, etc.) I didn’t use any.
Combine the sugar, water and vanilla bean seeds or extract in a small saucepan and warm over medium heat just until the sugar dissolves. Continue to cook, without stirring, until the syrup reaches 225◦F (107◦C) on a candy thermometer. Once it reaches that temperature, remove the syrup from the heat. While the syrup is heating, begin whisking the egg and egg yolk at high speed in the bowl of your mixer using the whisk attachment. Whisk them until they are pale and foamy.
When the sugar syrup reaches the correct temperature and you remove it from the heat, reduce the mixer speed to low speed and begin slowly (very slowly) pouring the syrup down the side of the bowl being very careful not to splatter the syrup into the path of the whisk attachment. Some of the syrup will spin onto the sides of the bowl but don’t worry about this and don’t try to stir it into the mixture as it will harden!
Raise the speed to medium-high and continue beating until the eggs are thick and satiny and the mixture is cool to the touch (about 5 minutes or so). While the egg mixture is beating, place the softened butter in a bowl and mash it with a spatula until you have a soft creamy mass. With the mixer on medium speed, begin adding in two-tablespoon chunks. When all the butter has been incorporated, raise the mixer speed to high and beat until the butter cream is thick and shiny. At this point add in your flavoring and beat for an additional minute or so.
Refrigerate the butter cream, stirring it often, until it’s set enough (firm enough) to spread when topped with a layer of cake (about 20 minutes).
For the white chocolate ganache:
ounces white chocolate 1 cup plus 3 tbsp. heavy cream Melt the white chocolate and the 3 tbsp. of heavy cream in a small saucepan. Stir to ensure that it’s smooth and that the chocolate is melted. Set aside to cool completely. In the bowl of a stand mixer, whip the remaining 1 cup of heavy cream until soft peaks form. Gently fold the whipped cream into the cooled chocolate to form a mousse. If it’s too thin, refrigerate it for a bit until its spread able. If you’re not going to use it right away, refrigerate until you’re ready to use.
For the chocolate ganache:
ounces plain chocolate, chopped 1 cup heavy cream Heat cream until simmering point and pour over the chopped chocolate. Stir until smooth and cool completely stirring occasionally until thickened.
Place the first cake on a serving platter, brush with syrup. Spread half of the butter cream over and then spread the white chocolate ganache carefully. (I only used three quarters of the mixture). Top with the other cake and brush also with syrup. Spread the rest of the butter cream and then spread the plain chocolate mixture carefully. Chill For the glaze:
ounces white chocolate, coarsely chopped ½ cup heavy cream.
Melt the white chocolate with the heavy cream. Whisk the mixture gently until smooth. Let cool for 10 minutes and then pour over the chilled cake. Using a long metal cake spatula, smooth out into an even layer. Place the cake into the refrigerator for 30 minutes to set.
Use melted chocolate to make any decorative pattern of your choice.