Put the milk, vanilla pods, vanilla seeds, lemon zest and half the cream into a small pan and slowly simmer for 10 minutes or until reduced by a third. Remove from the heat and stir in the soaked gelatine leaves until dissolved. Allow to cool a little, then place in the fridge, stirring occasionally until the mixture coats the back of a spoon. Remove the vanilla pods.
Whip together the icing sugar with the remaining cream. Mix the two cream mixture together. Divide into four serving moulds (I use little moulds, espresso cups or small glasses). Cover and chill for at least an hour.
Meanwhile chop the rhubarb into 4cm/1½inch pieces, sprinkle with the caster sugar and grill until lightly browned. Gently heat together the ginger, cinnamon and Champagne or Prosecco, then pour over the roasted rhubarb, cover, and leave for about 30 minutes for the flavours to do their bit.
To serve, sometimes I'll dip the mould or cup into some simmering water to loosen the pannacotta a little, then turn it out on to a plate next to some rhubarb with its juice (remove the cinnamon). Or you can just put the rhubarb on top of your cups or glasses of pannacotta and serve from there. Both ways are cool. Also gorgeous served with fresh figs and honey or caramelized blood oranges.
PS: Nice with a little basil.