1. Preheat the oven to 190°C/fan170°C/ gas 5. Grease, base line and flour a 23cm round, deep, loose-bottomed cake tin. Put the sugar and eggs into the bowl of an electric mixer. Whisk for 10 minutes, until pale and doubled in volume. Sift over the cornflour and flour and carefully fold in with a large metal spoon until just mixed. Pour into the tin and bake for 35-40 minutes, until risen and pale golden. Cool for 10 minutes, then turn out and cool completely. Store in an airtight container overnight - the cake will be easier to slice.
2. The next day, stone and slice the peaches and set aside 12 slices for decorating. Quarter 3 strawberries and chop the remainder. Reserve 6 raspberries, put the rest in a liquidiser with the icing sugar, and purée. Chill.
3. Make the custard cream. Put the milk, split vanilla pod and seeds in a pan and bring to the boil. Set aside. Mix the egg and sugar in a bowl until creamy. Stir in the flour, then whisk in the hot milk. Return to the pan and cook, stirring, over a medium heat for 2-3 minutes until thick. Discard the vanilla pod. Tip into a bowl, cover the surface with cling film to prevent a skin forming, and allow to cool.
4. In a separate bowl, whisk the cream to soft peaks. Mix half the cream into the cooled custard.
5. Cut the cake horizontally into 3 thin discs. Spread the bottom disc with a third of the purée and a third of the custard cream. Push in half the peaches and half the chopped strawberries, top with half the remaining purée and another cake disc. Spread with half the remaining custard cream, the remaining peaches and chopped strawberries and the rest of the purée. Finish with the top cake disc. Smooth the rest of the custard over the sides of the cake.
6. Push the almonds into the custard cream around the sides of the cake. Spread a little of the remaining double cream on top of the cake, put the remainder in a piping bag fitted with a star-shaped nozzle and pipe a swirl around the edge. Pipe a rosette in the centre, and arrange the reserved peach slices and strawberry quarters around it so they stand up. Arrange the reserved raspberries and blueberries on top. Chill and serve within 24 hours.
Tip: If you don't have an electric mixer, whisk the sugar and eggs in a bowl over a saucepan of simmering water for about 15 minutes. Cool before adding the flour. Store the decorated cake, chilled, for 1 day, or freeze undecorated for 1 month. Serve at room temperature.