Preheat the oven to Gas Mark 1-2, 130°C, 250°F, fan 110°C. Line a baking sheet with nonstick baking paper and draw a 23cm circle in the centre. Whisk the egg whites in a grease-free bowl until they form stiff peaks. Add half the caster sugar and whisk again until the mixture is thick and shiny. Mix the cornflour, vanilla and vinegar to a paste and fold into the eggs whites with the remaining sugar. Pile the meringue into the circle on the baking sheet, making a hollow in centre. Bake for about 1 1/4 -1 1/2hours or until pale brown but a little soft in the centre. Leave to cool. To make the raspberry sauce, mash 100g of the raspberries with the caster sugar, stir until the sugar dissolves. Now push the mixture through a nylon seive to remove the pips. Chill until required. Whip the cream until it forms soft peaks, heap in the centre of the meringue and top with the remaining fruit. Serve within 1 hour of filling.
