Pour 75 ml/3 fl oz. /5 tbsps. almost-boiling water into a heatproof bowl, then sprinkles the powdered gelatin. Stir until dissolved, then leave to cool. If using gelatin leaves cover the leaves with the water and leave for 20 minutes or until softened.
Pour the milk and cream into a heavy-based saucepan and add the vanilla pod/bean or add the vanilla extract together with the sugar. Bring to the boil, reduce the heat and simmer for 5- 8 minutes until the sugar has dissolved.
Remove from the heat and stir in the gelatin liquid in a thin, steady stream or add the softened leaves and stir until dissolved. Leave to cool.
Discard the vanilla pod and pour the milk mixture into four 150 ml/ ¼ pint/ 2/3 cup ramekins or small dishes. Chill in the refrigerator for at least 1 hour until set.
To serve:
Slide a sharp knife around the inside edge of each ramekin, place a plate over the top and tip it upside down to unmold it. Serve with a generous splash of Limoncello and a sprinkling of lemon zest.