Break the dark chocolate into small pieces and melt with 2 tbsp of water over a pan of simmering water. Stir until smooth and cool.

Beat the 2 egg yolks lightly, then stir into the cooled chocolate.

Whisk the egg whites until stiff peaks form, then gently fold into the chocolate mixture in stages. Cover and refrigerate.

Preheat the oven to 180°C (160°C fan). Lightly grease and line a 29cm x 18cm x 2.5cm Swiss roll tin with baking parchment.

In a large bowl, whisk the egg yolks until they begin to thicken. Gradually add the caster sugar and whisk until combined but not overly fluffy (about 1 minute).

Fold in the sifted cocoa powder until smooth.

In a separate clean bowl, whisk the egg whites to soft peaks. Gently fold them into the chocolate mixture.

Pour the batter into the prepared tin and bake for approximately 20 minutes. The cake should be springy to the touch and a skewer inserted in the center should come out clean.

Allow the cake to cool completely in the tin, where it will shrink slightly.

Turn the cooled cake out onto a parchment sheet dusted with icing sugar. Carefully peel off the original parchment.

Spread the chocolate mousse evenly over the cake, followed by a layer of whipped cream.

Roll the cake gently from the shorter end for a thicker roulade or the longer end for a thinner roll. Don’t worry if the cake cracks—it adds to the charm.