1.Start by placing the cream in a pan with the sugar, vanilla pod and lemon zest and juice. Cut the passion fruit in half, scoop out the seeds and pulp and pass them through a sieve. Add the passion fruit juice to the pan. Bring to the boil and boil for 1–2 minutes.
2.Leave the mixture to cool slightly. Have a taste just to make sure that the mixture isn’t too bitter. You can adjust the bitterness by adding extra sugar at this stage. Pour into 4–6 glasses (tumblers), depending on their size.
3.Chill for at least 1–2 hours, but overnight is best.
4.Pour the crème de cassis, blackberry balsamic vinegar and vanilla extract over the mixed berries in a container or bowl. Cover with cling film and shake. Leave for 1–2 hours, or overnight if possible, to infuse.
5.To plate, place the posset-filled glasses on a serving plate, spoon over some of the marinated berries and top with a mint sprig.