Rhubarb compote: Remove the tops and bottoms of the rhubarb, rinse and cut into pieces of 2-3 cm. Place the rhubarb in an ovenproof dish and stir in the sugar, vanilla pod and seeds, lemon zest and lemon juice. Bake at 150°C for 15-20 min. Set the baked rhubarb aside to cool. Green sugar: Rinse and dry the vervain leaves thoroughly. It is very important that the leaves are completely dry, otherwise the sugar will get wet and lumpy. Blitz the sugar and vervain leaves in a food processor into a green powder. Serve the baked rhubarb with lightly whipped cream and a sprinkle of green sugar on top.