Rub the butter into the flour and cocoa, and then stir in the sugar and egg yolk. Add iced water, if necessary, to bind to a pastry. Leave it to rest for half an hour, and then roll out, and line 4 pastry cases.
Bake blind for 6 to 8 minutes at 180°C/350°F/gas mark 4, remove from the oven, and leave to cool. You can make these a day or so in advance, if you wish.
Whisk the eggs and sugar until pale and much increased in volume. In a bowl set over a pan of hot water, melt the chocolate and butter.
Remove from the heat, and fold into the egg mixture.
Leave to cool, and then spoon into the pastry cases, and bake at 150°C/300°F/gas mark 2 in a preheated oven for 5 minutes.
Serve, dusted with icing sugar, or decorated with a small piece of gold leaf or thinly cut crystallized orange peel.
© 2000 Frances Bissell. All rights reserved.