Purée the raspberries and vanilla with the lemon juice and pass through a fine sieve.
Soak the gelatine in icy cold water for 4 minutes to soften it. Remove from the water and gently squeeze out any excess water then place in a clean bowl. Pour on 60 ml (4 Tablespoons) boiling water and stir to dissolve it thoroughly, then gradually stir in the berry purée until thoroughly mixed.
Melt the chocolate with 80 ml of the cream over a double boiler or in the microwave.
Lightly whip the remaining 220 ml cream with the sugar to form soft peaks then stir a quarter of this into the melted chocolate. Tip the chocolate mixture back into the whipped cream and fold it in. Add the berry purée, then fold this through making sure there are no lumps or streaks of purée. You can either pour this into a tub, to be quenelled later (as I did) or pour it into glasses or ramekins - whatever you’d prefer. Leave to cool, then cover and place in the fridge to set for at least 6 hours.