Put the milk, cream and caster sugar into a saucepan. Split the vanilla pod down its middle, scrape out the seeds, then add the seeds and the pod to the pan along with the bay leaves. Heat until the sugar dissolves then allow it to simmer gently for 3 mins. Take off the heat and set aside for 1 hour to let the flavours infuse.
Strain the milk/cream mixture through a sieve into another pan. Immerse the gelatine leaves in a bowl of very cold water for 5 mins, until they become soft and floppy. Squeeze the excess water out of them, then add to the infused milk/cream. Stir over a very low heat until the gelatine leaves have fully dissolved, then take off the heat.
Grease the espresso cups with vegetable oil. Divide the panna cotta mix between them, cover with cling film, and chill overnight or for at least 4 hours.
To make cardamom syrup, put the granulated sugar into a small pan along with the crushed cardamom pods and 60ml water. Heat until the sugar dissolves, then leave to cool and strain.
To serve: briefly dip the base of each pannacotta cup in boiling water and turn out onto a small plate or bowl. Use a sharp knife to prise away from the cup if necessary. Pour a little of the cardamom syrup over each and then decorate with edible flowers and lemon zest.