Lightly grease the insides of six 150ml/5fl oz ramekins with butter.
Put 3 tablespoons of the double cream in a small bowl, sprinkle the gelatine in an even layer over the surface and leave until spongy.
Put the remaining cream in a pan with the vanilla pod and sugar. Heat gently, stirring until almost boiling. Remove from the heat and discard the vanilla pod.
Whisk the gelatine into the cream mixture until dissolved. Pour into the ramekins, and chill for 2 hours.