Chocolate layer:
Break the dark chocolate into small pieces and place in a heatproof bowl.
Gently warm one half of the cream mixture, but do not boil it. It should be just warm enough to dissolve the gelatin.

Add the squeezed gelatine leaves to the warm cream mixture and stir well until completely dissolved.
Pour the warm cream mixture over the chocolate and stir until the chocolate is completely melted and the mixture is smooth.
Pour the chocolate mixture into dessert glasses or molds and leave to set in the refrigerator for at least 2 hours.

White panna cotta layer:
Gently warm the remaining cream mixture as described above and dissolve the remaining gelatine leaves.
Pour the mixture onto the set chocolate layer and leave to set again in the fridge for at least 2 hours.

Raspberry sauce:
Purée the raspberries with sugar and lemon juice in a blender or food processor until you have a smooth sauce.
Strain the sauce through a fine sieve to remove the seeds.

Serving:
Take the set panna cotta out of the fridge.
Pour the raspberry sauce over it or serve separately.
Garnish with fresh raspberries and chocolate shavings if desired