Step 1

Preheat the oven to 180°C, gas mark 4. Grease 2 x 20cm round sandwich tins with a little butter, then line the bases with baking parchment. In a small frying pan, gently toast the walnuts for the sponge over a low heat for 4-5 minutes, shaking the pan often, until they start to smell fragrant. Remove from the heat and allow to cool, then blitz in a small food processor or spice grinder until finely ground.

Step 2

Place the butter and caster sugar into a large bowl, or the bowl of a stand mixer. Beat with an electric mixer or the paddle attachment of the stand mixer for 5 minutes, until pale and fluffy. Add the eggs, one at a time, beating well after each addition, then add the flour, baking powder, toasted walnuts and coffee powder (or paste) and beat for 1 minute more. Using a spatula, scrape around the bowl a few times during the mixing process, to make sure it’s well combined.

Step 3

Divide the mixture evenly between the tins and use a spatula to smooth the top. Bake for 20-25 minutes, or until the cakes are risen and golden and a skewer inserted into the centre comes out clean. Cool for a few minutes, then turn onto a wire rack and allow to cool completely.

Step 4

For the icing, place the unsalted butter, icing sugar, salt and coffee paste together in a large bowl. Using an electric mixer, beat for a few minutes, or until pale and spreadable.

Step 5

To assemble the cake, pipe or spread half the icing in the middle and half on top, either piped into rosettes or using a palette knife to create swirls. Decorate with walnut halves and the chopped walnuts. This cake will keep for up to 3 days in an airtight container.