1 To make the compote, place the rhubarb, sugar and the lemon juice in a pot and bring to the boil. Simmer on a medium heat for around 7 min. Mix the cornflour with a little cold water and add to the rhubarb mixture. Remove from the heat and leave to cool.
2 To make the panna cotta, soften the gelatine in cold water. Place the vanilla pod, sugar and the cream into a pot and bring to the boil. Wring out the gelatine and dissolve in the warm cream mixture (do not allow to boil any more).
3 Remove the vanilla pod and beat the mixture over a cold bain marie. When the mixture begins to gel, fold in the yogurt and transfer the mixture to small bowls. Chilli for around 4 hours in the fridge and top with the compote to serve. Garnish with mint leaves.