Spoon the measured water into a small heatproof bowl or mug. Sprinkle the gelatine over and tilt the bowl or mug so that all the dry powder is absorbed by the water. Leave to soak for 5 minutes.
Pour the cream and milk into a saucepan, add the honey and bring to the boil. Add the soaked gelatine, take the pan off the heat and stir until completely dissolved. Add the rosemary and leave for 20 minutes for the flavours to infuse, stirring from time to time. Pour the cream mixture into 6 individual 150 ml (¼ pint) metal moulds, straining if preferred. Leave to cool completely, then chill for 4–5 hours until set.
Put all the compôte ingredients into a saucepan, cover and simmer for 10 minutes, then leave to cool.
Dip the moulds into hot water for 10 seconds, loosen the edges, then turn out the panna cottas on to small serving plates and spoon the compôte around them. Lightly dust the rosemary sprigs with caster sugar and use to decorate the panna cottas.