To make the panna cotta, first soak the sheets of gelatine in cold water for 10-15 minutes. Cut the vanilla pod lengthwise and scrape out the seeds with the tip of a knife. Pour the liquid cream into a saucepan and add the sugar.
Flavour with the vanilla seeds and add the pod; heat everything over low heat, without boiling; then, when the cream has reached boiling point, turn off the heat and remove the pod with kitchen tongs. When the gelatine has softened, drain it without squeezing too much, then soak it in the hot cream in the saucepan. Stir with a wooden spoon or hand whisk until the gelatine has completely dissolved; there should be no lumps. At this point, take four 150 ml moulds and ladle the panna cotta into them.
Once the moulds have been filled, place the panna cotta in the refrigerator and leave to set for at least five hours. To make removal from the mould easier, soak each mould in boiling water for a few moments, then turn out the panna cotta immediately onto individual serving plates. Serve the panna cotta alone, with caramel, melted chocolate or a fruit coulis.