Preheat the oven to 180 degrees Celsius (350 degrees Fahrenheit) Gas 4.

Whisk the egg whites and salt together until stiff but not dry and set aside. In a separate bowl, whisk the egg yolks and sugar together until pale, thick and mousse-like. Continue to whisk on low speed, while pouring the chocolate down the side of the bowl. Add a couple of spoonfuls of the egg whites and whisk vigorously to slacken the mixture slightly. Use a large metal spoon to fold the egg whites in, using a slicing action. Sift in the cocoa and fold until streak-free. Spoon the mixture into the prepared pan and gently level with a palette knife. Bake in the preheated oven for about 20 minutes, or until an inserted skewer comes out clean.

Upturn the cake onto a fresh piece of baking parchment while still warm with a clean kitchen cloth positioned underneath. Peel off the baking parchment from the base and carefully roll the cake up, using the kitchen cloth. Set aside to cool.

To make the filling, simply whip the cream until stiff but not dry, sift in the icing/confectioners’ sugar and fold.

Unroll the cold cake and spread the cream evenly over the top, leaving a small gap around the edges. Scoop out the passion fruit flesh and seeds and layer on top of the cream. Roll the cake up again, sift over some icing/confectioners’ sugar and transfer (seam side down) onto a serving plate.