Pour 900ml of the cream into a pan along with the vanilla pods and lemon rind, then bring to the boil. Turn the heat down to a simmer and cook until reduced by one-third

Meanwhile, soak the gelatine leaves in the milk for 15 minutes

Once the cream has reduced, remove the cooked lemon rind and set aside. Remove the vanilla pods and scrape the softened insides into the cream

Remove the gelatine from the milk and set aside. Bring the milk to the boil, then return the gelatine to the milk and stir until dissolved. Pour the milk and gelatine mixture into the hot cream through a sieve, stir, then leave to cool

Lightly whip the remaining cream with the icing sugar, then fold it into the cooled cooked cream. Stir in the grappa

Place a piece of cooked lemon rind in each of six small 200ml moulds or bowls. Pour in the cream mixture, cover with cling film and allow to set in the fridge for at least 2 hours

While the panna cottas set, cook the rhubarb. Preheat an oven to 150°C/gas mark 2 and cut the rhubarb into 6cm lengths, placing them in a small baking dish. Finely grate the zest of half the orange over the top of the rhubarb, then squeeze in the juice. Split the vanilla pods and scrape out some of the seeds to scatter over the top of the fruit, then place the vanilla pods in the baking dish too. Scatter over the sugar

Bake in the preheated oven for 15-20 minutes, until tender, then leave to cool in the dish

To serve, turn out the panna cottas onto dessert plates. Serve with the roasted rhubarb and its juices alongside, with an extra tablespoon of grappa poured over the top if desired