Heat the oven to 200C (180C fan)/390F/gas 6. Bash open the heads of garlic and remove the outer layers. Top and tail the fennel, remove the outer leaves if they are looking old (reserve the thick stalks for stocks or salads), then cut the bulbs in half and cut across into thick slices, no thicker than 1cm.
Heat a large, wide frying pan over high heat and a good glug of the oil. Saute half the garlic, fennel and leeks in the oil until rich and golden on all sides, then season generously and transfer to a wide baking dish large enough to hold everything later. Add another glug of oil and repeat with the rest of the vegetables (depending on the size of your pan, you may have to do this in more than two batches).
In a jug make up your vegetable stock and stir in the Essential yeast extract until dissolved. Scatter over the bay leaves, thyme (save some for the top) and lemon zest, then add your choice of white beans, mix well, pour in the wine and stock, and season.
Toss the breadcrumbs, chopped walnuts, parsley and parmesan with the reserved thyme leaves and scatter on top.
Drizzle with the remaining oil, cover with foil and bake for 45 minutes. Uncover, bake for 15-20 minutes more, until the top is golden, crusty and looking tempting, then remove and leave to rest for 10 minutes. Serve with a salad.