Peel the stalks from one artichoke, then cut the top one-third from the bulb and discard. Immediately rub the artichoke all over with the intact half of the cut lemon to stop it from browning. Repeat the process with the remaining artichokes.
Bring 200ml/7fl oz of water and all of the olive oil to the boil in a lidded saucepan. Reduce the heat until the mixture is simmering.
Cut the artichokes in half lengthways and add them to the pan. Cover the pan with the lid and simmer for 10-15 minutes, or until the artichokes are tender (when you pierce them with the tip of a knife there should be no resistance).
Remove the artichokes from the pan using a slotted spoon and set aside to cool slightly, then cut in half again lengthways.
Meanwhile, heat the butter in a frying pan over a medium heat. When the butter is foaming, add the shallots, garlic and thyme and fry for 1-2 minutes, or until softened but not coloured.
Add the rice and stir well to coat it in the butter. Cook for a couple of minutes, then pour in the white wine and bring the mixture to the boil. Reduce the heat until the mixture is just simmering.
Add a couple of ladlefuls of stock to the pan at a time and return the mixture to a simmer each time, stirring occasionally, until the rice has absorbed all the stock. Continue adding stock and letting the rice absorb it for 5-6 minutes, then stir in the broad beans and continue to add ladles of stock until the stock has been absorbed by the rice, the mixture is loose and the rice is tender; this should take 12-15 minutes.
When the rice is cooked through, add the artichokes, parmesan, chives, lemon zest and juice, and cream. Season, to taste, with salt and freshly ground black pepper.
Serve the risotto with extra parmesan grated over the top, and garnished with the chive flower leaves, if using.