• 400 g (14 oz) good-quality dark chocolate, broken up
• 6 eggs, separated
• 150 g (5½ oz/⅔ cup) caster (superfine) sugar
• 2½ tablespoons Cointreau
• 300 ml (10½ fl oz) pure (whipping) cream, plus extra, whipped, to serve
• icing (confectioners’) sugar, to serve

Preheat the oven to 175°C (345°F/Gas 3). Cut a piece of greaseproof paper to fit a 20 cm (8 inch) round cake tin, with a double layer for the side and a single layer for the bottom. Spray the tin with cooking oil and fit the greaseproof paper in snugly.

Melt the chocolate in a stainless steel bowl set over a saucepan of hot water. Don’t let the water in the saucepan boil, as you can scald the chocolate. Remove the chocolate from the heat and allow to return to room temperature.

In a large bowl, beat the egg yolks and two-thirds of the sugar until pale and creamy. Add the Cointreau and continue to beat until well combined. Add the chocolate to the egg yolk mixture and stir until completely incorporated, then slowly stir in half the cream. Set aside. Whip the remaining cream until soft peaks form. Set aside. Start whisking the egg whites in a very clean bowl. When soft peaks start to form, slowly add the remaining sugar and whip until very firm. Fold the whipped cream into the chocolate mixture. Finally, fold in the whipped egg whites.

Pour into the cake tin, put the tin in a bain-marie or on a baking tray and add enough hot water to come about 2.5 cm (1 inch) up the outside of the tin. Bake for 45 minutes. Turn the oven down to 150°C (300°F/Gas 2) and bake for a further 45 minutes. Turn the oven off and leave the cake in the oven for 20 minutes. Cut around the edge of the tin, turn it over onto a plate and the cake should slide out easily. Cut slices using a knife dipped in hot water and clean the knife after each cut. Place on white plates. Sprinkle with icing sugar and serve with lightly whipped cream.