Soak the gelatine ina small bowl of cold water for 5 minutes until soft. Squeeze out the liquid and tip out all but 1 tablespoon of water.
Put the gelatine into a heatproof bowl with the tablespoon of water. Put the bowl over a pan of simmering water for a few minutes. Stir until dissolved and runny.
Blend the raspberries in a food processor and pass through a sieve into a bowl, removing the seeds.
Whisk the yolks and caster sugar together in a bowl using an electric hand whisk until thick, fluffy and pale in colour. This will take about 4–5 minutes.
Whip the cream to soft peaks in a separate bowl.
Stir the sieved raspberries and gelatine into the egg yolk and caster sugar mixture, then carefully fold in the cream.
Whisk the egg whites in a clean bowl until stiff peaks form. Stir 2 tablespoons into the raspberry mixture, then carefully fold in the rest.
Spoon into a 1.2 litres/2 pint bowl or 4–6 glasses. Place in the fridge for 4 hours, or until set.
Decorate with raspberries and serve straight from the fridge.