Preheat the oven to 190°C/Gas 5. Butter two 20cm loose-based sandwich tins and line the bases with discs of baking parchment. Put the walnut halves in a food processor and blitz them into fairly fine crumbs, but don’t worry if there are a few larger pieces remaining. Tip the walnuts into a bowl.
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Step 2
Put the butter, sugar, eggs, flour, baking powder and coffee essence in a food processor and blend on the pulse setting until well combined and creamy. You may need to remove the lid once or twice and push the mixture down with a rubber spatula. Take care not to process for too long or you will end up with a heavy sponge. Add the blitzed walnuts to the batter and mix until just combined. If you don’t have a food processor, finely chop the nuts, tip all the ingredients into a large mixing bowl, then beat like hell!
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Step 3
Spoon the mixture evenly into the greased and lined tins and smooth the surface. Bake on the same shelf in the centre of the oven for about 25 minutes or until the sponge is well risen and just beginning to shrink back from the sides of the tin.
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Step 4
Remove the tins from the oven and leave to cool for 5 minutes before running a knife around the edge of the cakes and turning them out onto a wire rack. Peel off the baking parchment and leave to cool completely.
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Step 5
To make the icing, put the butter in a food processor, or mixing bowl, then add the icing sugar and coffee essence. Blend until the icing is smooth and creamy. Add a little more coffee essence to taste if you like.
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Step 6
Place one of the sponges on a plate or cake stand and spread with half the coffee icing. Add the second sponge and spread the remaining icing over the top. Use the back of a spoon or a rubber spatula to create soft swirls and peaks. Decorate with the walnut halves. Leave to stand for at least an hour before serving if possible to allow the icing to become a little firmer.
Ingredients
Sponge
65 g walnut halves
225 g softened butter, cubed, plus extra for greasing