Fold a sheet of greaseproof paper in half and then wrap round a 1.5 litre souffe dish to make a 5cm collar above the rim of the dish. Secure with sellotape and paperclips. Blend together the strawberries and lemon juice until smooth in a blender. Crack the egg yolks into a large bowl, add 100g of caster sugar and whisk with an electric whisk for at least 5 minutes or until the mixture is pale and thick, doubled in volume and it leaves a ribbon trail on the surface of the mixture.
Soften the gelatine leaves in cold water for a few minutes and then squeeze out the excess water. Place the softened gelatine into a small bowl that fits snugly over a pan of gently simmering water and leave to melt. Remove from the heat and whisk into the egg mixture and then fold in the strawberry puree and pass through a sieve into another bowl. Softly whip the double cream with the vanilla seeds and fold this into the strawberry mix.
Whisk the egg whites until they form soft peaks and then gradually add the remaining sugar a little at a time until you have a thick glossy meringue. Fold the meringue mix into the raspberry mix and pour into the prepared soufflé dish. Chill overnight and then carefully remove the paper collar and decorate with the reserved strawberries dotted around the edge of the soufflé and dust with a scattering of icing sugar.
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