Walnut cake with American frosting

1. Preheat the oven to 180ºC (350ºF), Gas mark 4. Brush the cake tins (two 20cm (8in) diameter or three 18cm (7in) diameter sandwich tins) with melted butter and dust with flour. Line the base of each with greaseproof or parchment paper.
2. Sift the flour with the salt and baking powder. Cream the butter in a large bowl or in an electric food mixer until soft. Add the sugar and vanilla extract and beat until the mixture is light and fluffy. Beat in the egg yolks and then stir in the chopped walnuts. Fold in a quarter of the flour and milk into the mixture, alternating each, until they are incorporated.
3. In a separate bowl, whisk the egg whites until they are stiff.
4. Stir a quarter into the cake mixture and then gently fold in the rest. Divide between the tins, making a slight hollow in the centre of each so that the cake rises evenly rather than forming a peak.
5. Bake in the oven for about 16–20 minutes until firm to the touch or until a skewer inserted into the centre of each cake comes out clean. Remove from the oven and allow to sit for 5 minutes before turning out onto a wire rack to cool.
6. Meanwhile, make the buttercream filling. Cream the butter until very soft, then beat in the icing sugar and the vanilla extract. When the cake is cold, sandwich the layers together with the filling.

Make the American frosting

1. Ensure your cake is ready before you start, as this icing begins to set very quickly. Bring to the boil a saucepan of water large enough to hold a heatproof bowl. Place the egg whites in the bowl and whisk with a hand-held electric beater until very stiff.
2. In a separate saucepan over a medium-high heat, dissolve the sugar in the water and boil for 5-10 minutes until the liquid is thick and syrupy and has reached the 'thread' stage - when the last few drops that fall from a metal spoon dipped into the syrup come off in one long, quite thick and syrupy thread.
3. Pour the boiling syrup over the stiffly beaten egg whites, whisking all the time with the hand-held beater. Place the bowl in the saucepan of simmering water. Continue to whisk over the water for 10-15 minutes until the icing is snow white, very thick and meringue-like.
4. Spread quickly over the cake with a palette knife, regularly dipping the knife into a jug of boiling water to help spread the icing. It sets very quickly at this stage, so speed is essential.
5. Scatter with rose petals, if using, or arrange the walnut halves around the top of the cake, and allow the icing to set until it feels dry on the surface.