Put 1 tablespoon hot water in a small heatproof bowl, sprinkle the gelatine over the top and leave until spongy. Bring a small pan of water to the boil, remove from the heat and put the bowl into the pan. The water should come halfway up the side of the bowl. Stir the gelatine until dissolved.
In a large bowl, stir the vanilla yogurt and fromage frais together to combine, then add the cooled gelatine and mix well.
Using an electric beater, beat the egg whites until stiff peaks form, then fold through the yogurt mixture until just combined.
Gently fold the raspberries through the mixture. Chill for several hours before serving.