1. Preheat the oven to 180C/350F/Gas 4. Place the butter into a large mixing bowl and beat until light and smooth. Add the sugar and cream together until light and fluffy.
2. One at a time add each egg making sure to beat well to completely incorporate each egg before adding the next egg. If the mixture looks like it's about to curdle add 1 spoonful of the flour. Then add the dissolved coffee to the mixture and mix well.
3. Add the flour and chopped walnuts and gently fold in until fully combined.
4. Divide the mixture into two 20cm/8 cake tins which should be greased / lined with parchment paper. Transfer to the oven to bake 25-30 minutes, or until a skewer inserted into the centre of the cake comes out clean and the cake is golden-brown. Remove the cakes from the oven and leave to cool on a wire rack.
5. Whilst the cakes are cooling make the butter icing. Firstly beat the butter in a small bowl until pale and smooth then gradually beat in the icing sugar. Next add the espresso and mix well.
6. Split the butter icing mix in half and spread one half on to the flat side of one sponge. Then place the second sponge on top. Finally add the reaming butter icing to the top sponge.