Preheat the oven to 180°C/ Gas mark 4 and line a 20x10cm (8x4in) deep loose-bottomed cake tin.

Melt the butter and chocolate in a bowl set over a pan of simmering water, stirring occasionally. While the chocolate is melting, whisk the egg yolks with half the sugar in a large bowl, until pale, thickened and doubled in volume.

In a separate bowl, with clean whisks, whisk the egg whites until stiff, then gradually beat in the remaining sugar, 1 tbsp at a time, whisking after each addition. You should by the end have a stiff, glossy mix.

Fold the melted chocolate and butter into the egg yolk and sugar mixture, followed by the egg white mix in batches. Pour the mixture into the prepared 5 tin and bake for 60-75 minutes, or until a skewer inserted in the centre comes out with just a few moist crumbs clinging to it. Leave the cake to cool in the tin. It will sink in the middle, but this is completely normal.

Once the cake has cooled, remove from the tin and spoon the crème fraiche in to fill the sunken centre of the cake. Finally, pile on the strawberries, raspberries and a few mint leaves. To finish, dust over a little icing sugar.