Sift the cocoa powder and flour together, and fold gently into the egg and sugar mixture. Stir in the coffee or liqueur.
Whisk the egg whites with the remaining sugar and fold into the cake mix. Pour into the Swiss roll tin, level it off, and
To prepare the filling, put the chocolate and liqueur in a clean pudding basin over hot water, and melt the chocolate. Remove from the heat, cool slightly, and mix in the softened butter. Whisk the egg yolks and sugar until pale and ribbony. Whisk the egg whites with a pinch of salt until stiff, and fold both into the chocolate.
Cover with clingfilm, and freeze for several hours until set. Turn out onto a board, slice, and serve on individual plates with a spoonful of crème fraiche or a dash of coffee liqueur, and a dusting of icing sugar.
© 2000 Frances Bissell. All rights reserved.