Step 1

Make the Joconde: Preheat oven to 350°F / 175°C. Generously grease an 11 by 16-inch / 41 by 28cm jelly-roll pan, then line the bottom with greased parchment paper.

Step 2

In a large bowl, sift together the all-purpose flour and almond flour. Set aside.

Step 3

In a stand mixer fitted with the whisk attachment, whip the eggs and 1/2 cup / 100g sugar on high speed for about 8 minutes. The batter should be very light in color and texture. When you lift the whisk out of the mixture, the batter should form a ribbon that sits on the surface of the egg foam for several seconds. Turn the speed to medium and continue to whip for 1 minute more. Remove the bowl from the mixer and, using the whisk attachment or a rubber spatula, gently fold the almond mixture into the egg foam in three additions.

Step 4

In a clean mixer bowl with a clean whisk attachment, whip the egg whites and salt on medium speed just until they start to foam. Slowly sprinkle in the remaining 2 tablespoons sugar to create a French meringue, then whip on high speed until glossy, stiff peaks form, 1 to 2 minutes. Remove the bowl from the mixer and, using the whisk attachment or a rubber spatula, gently fold the meringue into the almond batter.

Step 5

Pour the batter into the prepared pan and spread evenly with an offset spatula. Bake until the cake is set and just golden on top, 12-15 minutes. Let the cake cool completely in the pan.

Step 6

Make the buttercream: In the bowl of your stand mixer fitted with the whisk attachment, combine the sugar and egg yolks and beat on medium speed to mix. The mixture will be very thick and grainy.

Step 7

Put 1 inch / 2.5 cm of water in the bottom of a double boiler or a medium saucepan and bring to a gentle simmer over medium-low heat. Place the bowl with the yolk mixture over the simmering water and stir the mixture with a rubber spatula until the sugar is completely melted. Brush down the sides of the bowl with the spatula to make sure all the sugar is melted. Feel the mixture between your fingers to check for graininess. Once all the sugar has melted and the mixture is smooth, the syrup is hot enough (140°F / 60°C) to be safe to consume.

Step 8

Return the bowl to the stand mixer fitted with a clean whisk attachment and beat on medium-high speed until the egg foam is light, fluffy, and glossy and the bowl feels just about room temperature. (If the egg foam isn't cooled sufficiently, the butter will melt when you add it.)

Step 9

Once the egg foam is whipped and cooled, turn the mixer to medium speed, add the butter, 2 tablespoons at a time, and beat until incorporated. Turn the speed to low, add the vanilla and salt, and mix until incorporated.

Step 10

Combine the buttercream and blackberry preserves and stir until very smooth.

Step 11

Make the ganache: In a medium saucepan over low heat, warm the cream until just simmering. Turn off the heat and add the chocolate. Swirl the pan to make sure all of the chocolate is submerged in the hot cream. Let sit for 3 minutes and then gently stir until smooth. Keep in pot until ready to use. You want the ganache to be a pourable consistency but not so warm that it will melt the buttercream.

Step 12

Assemble the cake: Using an offset spatula, spread the buttercream evenly over the cake. Transfer to the refrigerator and let set until solid, about 20 minutes. Remove the cake from the refrigerator, pour the ganache over the chilled buttercream. Refrigerate again until all layers are solid, about 45 minutes.

Step 13

Remove the cake from the refrigerator, run a knife all the way around the edges of the cake to loosen from the pan, cover with plastic wrap (this will protect the ganache when the cake is inverted), and invert the cake onto the back of a second baking sheet. Peel the parchment from the bottom of the cake and invert again onto a large cutting board.

Step 14

Using a chef's knife, cut the cake in half on the long side and then in three equal sections from the short side, so you have six identical rectangles. Stack the six sections so you have a tall cake with many layers, making sure the layers are straight. Using a knife dipped in hot water, trim any uneven cake. (At this point, you can store in the refrigerator, covered, for up to 48 hours).

Step 15

Make the meringue (prepare just before decorating and serving the cake): In a medium saucepan over medium-low heat, bring 1 inch / 2.5cm of water to a simmer.

Step 16

In the bowl of a stand mixer, combine the egg whites, sugar, and salt; place over the simmering water; and stir with a rubber spatula until the mixture is hot and all of the sugar has dissolved, about 5 minutes.

Step 17

Remove the bowl from the heat and place onto the stand mixer fitted with the whisk attachment, then beat on high speed until very thick and glossy and stiff peaks form, about 5 minutes. If the meringue is not stiff enough, your spikes will slouch and lose the drama. Add the vanilla and mix well.

Step 18

Take a blob of the meringue topping between your fingers and press it against a blackberry. Pull the blob away, it will break off in a wispy curl. Repeat with the remaining meringue and blackberries. Using a kitchen blowtorch, toast the tops of the meringue.