Bring the buttermilk, cream and sugar to the boil, reduce the heat, reduce to approx. 400 ml. Remove the pan from the heat. Add the gelatine, stir, pour the mixture through a sieve into a measuring cup. Transfer the mixture to the prepared ramekins, leave to cool, cover and leave to set in the fridge for approx. 4 hrs.
Mix the rhubarb, wine, sugar, vanilla pod and seeds in an ovenproof dish (approx. 2 l).
Approx. 15 mins. in the centre of an oven preheated to 200°C. Remove and allow to cool a little.
Carefully slide the tip of a knife around the edges of the panna cotta. Briefly dip the ramekins in hot water and turn out the panna cotta onto plates. Top with the rhubarb and biscuits.