For the sponge in the coffee cake, you will need:

200g self-raising flour
4 eggs
200g softened butter
200g golden caster sugar
1 tsp baking powder
2 tbsp instant coffee granules
water
handful of chopped walnuts

And for the icing:

200g softened butter
300g icing sugar

Using an electric whisk, beat the caster sugar and butter together until light and fluffy. Then add the baking powder, eggs and flour, a little at a time, whisking thoroughly in between. Mix the coffee granules in 100ml of water. Stir 2 tbsp of this mixture and the walnut into the cake mixture. Bake in a pre-heated oven at 180°C (350°F) – 150°C (300°F) if fan assisted – for 40 minutes.

Test if the cake is cooked by inserting a pin or fork in the middle. If it comes away clean, it is cooked. If not, return to the oven 5 minutes at a time until cooked. Turn out to cool.

For the icing, whisk together the butter, icing sugar and as much of the coffee mixture as needed to give you the flavour you want.

Slice the cooled cake in half horizontally and spread half the icing over the bottom half. Replace the top half and spread the remaining icing over the top.