Thoroughly grease a Non-Stick Traybake then line with parchment.
Measure all the sponge ingredients into a large bowl and beat until well blended. Turn the mixture into the prepared tin and level the top.
Bake for about 35-40 minutes or until the cake has shrunk from the sides of the tin and springs back when pressed in the centre with your fingertips. Leave to cool in the tin
To make the icing, beat together the butter with the icing sugar, milk and coffee extract. Spread evenly over the cake using a palette knife then decorate with the chopped walnuts.