Heat the oven to 170°C/Gas 3½. Heat a little olive oil in a large casserole pot and gently cook the onion, carrot, celery and garlic over a low heat until beginning to soften and take a little colour, about 15 minutes.
Remove from the pan and set to one side. Season the lamb with salt and pepper. Turn the heat up to medium, add some more oil to the pan and brown the lamb on all sides. When nicely golden, add the wine and scrape the base of the pan with a wooden spoon to deglaze.
Cook until the wine is reduced by half. Return the veg to the pan, add the bay leaf and pour in the stock so that the lamb is just covered. Season with salt and pepper, cover the casserole and transfer to the oven for 30 minutes.
Cut the turnips into thick wedges, add to the casserole and cook for a further hour, or until the lamb is tender. Add the French and broad beans to the pot and simmer on the stove for about 5 minutes to cook them.
Just before serving, stir in the mustard, parsley and mint leaves and a squeeze of lemon juice.
* Use a jointed chicken or duck legs or diced shoulder of lamb instead of the neck. Shoulder will take longer to cook, 30 minutes or so extra, so add the beans and turnips later – after 1 hour.
* Or omit the meat: brown the turnips in place of the lamb and use vegetable stock; add a handful of pearl barley, spelt or bulgur wheat and simmer until the turnips are tender, about 30 minutes.