• 220 g self-raising flour
• 1 tsp baking powder
• 220 g soft butter or margarine
• 220 g caster sugar
• 4 eggs
• 60 g walnuts, chopped
• 2 tsp instant coffee granules dissolved in 1 tbsp boiling water

For the filling and frosting:
• 90 g softened butter
• 250 g tub mascarpone
• 1 tsp instant coffee granules dissolved in 2 tsp boiling water
• Approx. 350 g icing sugar
• Walnut halves to decorate

Preheat the oven to 190ºC and grease and line the bases of two 20-cm sandwich cake tins with baking paper or greased greaseproof. Sift the flour and baking powder into a mixing bowl, add the butter, caster sugar, and eggs and beat them together with an electric whisk for at least two minutes, scraping down the bowl from time to time. Stir in the chopped nuts and dissolved coffee and divide the mixture between the tins, spreading it evenly. Bake for about 25 to 30 minutes until springy to the touch and shrinking away from the sides of the tin. Cool in the tins for 10 minutes, then turn out on to a rack and peel off the paper. When they are cold, cut each cake horizontally in two.

For the filling and frosting: Beat the butter and mascarpone together until well blended, then stir in dissolved coffee. Sift in the icing sugar, a tablespoon at a time, and beat well after each addition until you have a nice fluffy, spreadable mixture, about the consistency of whipped cream. Sandwich the cakes together with some of the frosting, then swirl the rest over the top and sides of the cake and decorate with the walnut halves. Transfer to a serving dish and chill in the fridge until the icing is set.