JocondeNote: The joconde can be made up to 1 day in advance and kept wrapped at room temperature
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 it aside.
If you only have one bowl, wash it after removing the egg whites or if you have a second bowl, use that one. Attach the paddle attachment to the stand mixer (or using a handheld mixer again) and beat the almond flour, icing sugar and eggs 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 overmix 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 heat-proof 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.
Simple Syrup(Note: The syrup can be made up to 1 week in advance and kept covered in the refrigerator.)
Stir all the syrup ingredients together in the saucepan and bring to a boil.
Remove from the heat and let cool to room temperature.
Buttercream:Put the sugar and egg whites in the medium heatproof bowl and fit the bowl over a plan of simmering water. Whisk the mixture constantly over medium heat, until it feels hot to the touch, about 3 minutes. The sugar should be dissolved, and the mixture will look like shiny marshmallow cream. Remove the bowl from the heat.
Working with the whisk attachment, beat the meringue on medium speed until it is cool, about 5 minutes. Switch to the paddle attachment and add the butter a stick at a time, beating until smooth. Once all the butter is in, beat the buttercream on medium-high speed until it is thick and very smooth, 6-10 minutes. During this time the buttercream may curdle or separate – just keep beating and it will come together again.
On medium speed, gradually beat in the orange juice, waiting until each addition is absorbed before adding more, and then beat in the vanilla. You should have a shiny velvety smooth buttercream. Stir in orange zest. Press a piece of plastic against the surface of the buttercream and set aside briefly.
White Chocolate Ganache Mousse:(Note: The mousse can be made ahead and refrigerated until you’re ready to use it.)
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. Add the tablespoon of liqueur to the chocolate and stir. 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 it’s spreadable.
If you’re not going to use it right away, refrigerate until you’re ready to use.
Orange GlazeNote: It’s best to make the glaze right when you’re ready to finish the cake.
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.
Assembly(Note: The finished cake should be served slightly chilled. It can be kept in the refrigerator for up to 1 day).
Line a baking sheet with parchment or wax paper.
Working with one sheet of cake at a time, cut and trim each sheet so that you have two pieces (from each cake so you’ll have four pieces in total): one 10-inch (25-cm) square and one 10 x 5-inch (25 x 12½-cm) rectangle.
Place one square of cake on the baking sheet and moisten it gently with the flavoured syrup.
Spread about one-half of the buttercream over this layer.
Top with the two rectangular pieces of cake, placing them side by side to form a square. Moisten these pieces with the flavoured syrup.
Spread the remaining buttercream on the cake and then top with the third square of joconde. Use the remaining syrup to wet the joconde and then refrigerate until very firm (at least half an hour).
Prepare the ganache/mousse (if you haven’t already) and then spread it on the top of the last layer of the joconde. Refrigerate for at least two to three hours to give the ganache/mousse the opportunity to firm up.
Make the glaze and after it has cooled, pour/spread it over the top of the chilled cake. Refrigerate the cake again to set the glaze.
Serve the cake slightly chilled