• Line an 8x4x2 loaf tin with clear film (saran wrap), allowing it to overlap the sides and ends. Break the chocolate into a small heat-proof bowl and place over a saucepan of simmering water (not boiling) until melted. Make sure the bowl does not touch the water. Stir until smooth. Remove the bowl from the pan and allow to cool slightly.
• In a mixing bowl, cream the butter until smooth. Slowly add the confectioner’s sugar and beat until combined. Separate the eggs, beating the yolks into the creamed butter one at a time.
• Add the vanilla extract and melted chocolate and mix well. Beat the egg whites until stiff. Fold one-third of the beaten whites into the chocolate mixture to lighten it, then gently fold in the remainder.
• Spoon the mixture into the prepared loaf tin and spread evenly. Chill until firm for at least 4 hours or until set.

For the Chocolate Sauce

• Meanwhile, measure 1/4 pint of water (about half a cup) and the caster sugar for the chocolate sauce. Stir over low heat until the sugar has dissolved and the syrup is boiling. Add the cocoa powder and whisk until smooth. Cool.
• When ready to serve, lift the Chocolate Marquise and invert it onto a serving plate. For easier cutting, use a non-serrated knife that's been dipped in warm water. Drizzle with the chocolate sauce and top with some sugar-dusted raspberries. Glazed apricots and fresh strawberries can also be served with this sweet and chocolatey dessert for sharpness of flavour and colour contrast.