Soak the gelatine in cold water according to the instructions on the packet. Wash the strawberries and raspberries. Put together in a blender and puree.
Strain the mixture through a fine sieve. Then heat with the sugar and lemon juice in a small saucepan. Remove from heat and stir in the squeezed gelatine. Let cool down.
Whip the cream until stiff, pull it into the fruit puree and pour into a piping bag. Splash into four glasses and chill for at least 3 hours.