Step 1

Preheat the oven to 325°F (165°C) and butter a 9-inch (23cm) springform pan. Set aside.

Step 2

Over a double boiler or the microwave, heat the chocolate, butter, vanilla extract and salt until melted. Allow to cool down for 10 minutes.

Step 3

Whisk the egg yolks in the cooled, chocolate mixture and set aside.

Step 4

In a stand mixer or large bowl, whip the egg whites on medium-high speed until soft peaks, and then add sugar, one spoon at a time, and whip until stiff peaks form.

Step 5

With a metal spoon, fold half of the egg whites in the chocolate mixture until mostly combined, then add the remaining egg whites and fold in until evenly mixed.

Step 6

Pour the batter into your prepared pan and bake until the edges are done and the center is just set, about 14-16 minutes. Set aside and allow to cool completely for at least 1 hour. (do not remove from the pan).

Step 7

Over a double boiler or in the microwave, heat the bittersweet chocolate, water and cocoa powder until melted and dissolved. Set aside to cool for 10 minutes.

Step 8

Once cooled, whip the cream on high speed to medium-soft peaks, and then fold into the chocolate mixture until evenly combined.

Step 9

Spread the bittersweet chocolate mousse over the cooled chocolate cake and refrigerate while you make the top layer.

Step 10

In a small bowl add the water and sprinkle over the gelatin without stirring. Let bloom for 5 minutes to set.

Step 11

Over a double boiler or in the microwave, gently melt the white chocolate with ½ cup (4floz/120ml) heavy cream and the bloomed gelatin and then let white chocolate mixture cool for 10 minutes.

Step 12

Once cooled, whip the remaining 1 cup (8 fl oz/240 ml) heavy whipping cream on high speed to medium-soft peaks and then fold the white chocolate mixture.

Step 13

Spread the white chocolate mousse on top of the dark chocolate mousse and smooth out the top with an offset spatula. Cover and return to the refrigerator to chill for at least 4 hours and up to 3 days.

Step 14

Just before serving, run a thin knife around the edge of the cake and release the sides. Carefully loosen the bottom of the cake with an offset spatula and transfer to a serving plate. Tidy the sides a little with a knife so you can see each layer. Garnish with the chocolate shavings. Enjoy!