Method

1. For the cake: preheat the oven to 180C/gas 4. Line a large Swiss roll tin with baking parchment.

2. Cream together the butter and the sugar with an electric hand whisk until pale and creamy. Beat in the eggs one at time, incorporating well before adding the next one. Don't worry if the mixture splits, add a tablespoon of flour and mix well.

3. Fold in the flour, baking powder and coffee. If the mixture is a little thick add some milk or a little more coffee. You want the mixture to be a dropping consistency, that is when you take a spoonful of the mixture you can drop the mixture from the spoon in one big blob with a sharp tap of the spoon.

4. Spread the mixture into the prepared tin and cook for 20-30 minutes or until a skewer comes out clean from the cake. If it starts to get a little brown before it is cooked cover the top with foil. Turn the cake out onto a cooling rack and leave to cool completely.

5. For the praline: put the sugar in a shallow saucepan with the water. Heat until the sugar is melted and turns a light caramel colour. Do not stir the sugar, but if needs be you can swirl the pan.

6. Add the walnuts to the caramel and turn to coat evenly. Tip out onto an oiled baking tray or silicone mat. Use an oiled spoon to separate 20 nicely shaped walnut halves, and set aside for decoration. Once cooled, blitz the remaining walnut praline in a food processor until coarsely ground.

7. For the icing: beat the butter and icing sugar together. Beat the coffee in, a little at a time until you have the desired strength. If the icing becomes too soft, add a little more icing sugar.

8. Cover the top of the cooled coffee cake with the icing and sprinkle with the walnut praline. Refrigerate until the icing has set then cut into 20 squares. Finishing each square with a sugar-coated walnut half.