Preheat the oven to 170°C/150°C fan oven/Gas Mark 3. Grease and baseline a 23 cm (9 in) springform cake tin with non-stick baking parchment. Put the walnuts and flour in a food processor and whiz to a fine powder. Put to one side. If you don't have a food processor, grind the nuts through a drum nut grater or cheese grater and mix them with the flour.

Separate the eggs, then put the yolks in the bowl of a food processor and five whites in a large mixing bowl. (Freeze the remaining whites for use later.) Add the sugar to the yolks and beat until pale and very thick. Alternatively, whisk together the egg yolks and sugar in a heatproof bowl over a pan of simmering water with an electric hand whisk.

Using a metal spoon, fold the walnut and flour mixture into the yolk mixture. Whisk the egg whites to soft peaks. Fold in one-third of the egg white to the yolk mixture, then carefully fold in the rest. Pour the mixture into the lined tin.

Bake the cake for 55 to 60 minutes or until a skewer inserted into the

centre for 30 seconds comes out clean. Cool in the tin for 15 minutes,

then turn out on to a cooling rack.

To make the filling, dissolve the coffee in the boiling water and put to one side. Put the butter in a bowl and beat until very soft and creamy. Gradually beat in the icing sugar and 4 teaspoons of the dissolved coffee (reserve the rest) until well combined and fluffy.

Cut the cake horizontally into three layers. Put the bottom layer on a serving plate and spread half the coffee filling over it. Gently press the second layer into position and spread with the remaining filling. Lift the top of the cake into position and press down gently.

For the icing, put the icing sugar into a bowl, add 1/2 to 1 teaspoon of the reserved coffee and 2 to 3 tablespoons of boiling water and combine thoroughly. Pour the icing on the cake then, with a round-bladed palette knife, quickly spread in an even layer to the edge, then decorate with walnut pieces. Allow the icing to set (about 2 hours) before serving.The cake will keep for about five days.