Whole roasted stuffed onions with cream, parmesan and mushrooms

Serves 6 Prep time 30 mins, cook 1 hr 20 mins This recipe is inspired by one by Nigel Slater. It's important to keep the onion shells intact when removing the insides.

Cook onions in a large saucepan of simmering salted water over low-medium heat until tender (20-30 minutes). Drain, then, when cool enough to handle, cut 2cm from top of each onion. Remove excess onion from inside tops with a small sharp knife and set tops aside (discard excess onion). Score centres of onion bases, then remove inside of onion with a knife so that a thick layer of onion remains to form a shell (do not pierce the shell; discard two-thirds of the excess onion). Finely chop remaining onion, set aside.

Preheat oven to 180C. Heat butter in a frying pan over medium heat, add reserved chopped onion, pancetta, field mushroom, porcini and garlic and saut until tender (8-10 minutes). Transfer to a bowl and set aside to cool, then add double cream, parmesan, breadcrumbs, thyme and lemon rind and season to taste. Spoon into onion skins, then place reserved tops on onions (you may have some mixture left over). Place in a baking dish to fit onions snugly. Pour over pouring cream, scatter with thyme sprigs. Bake until golden and warmed through (40-50 minutes; scatter with extra parmesan during last 10 minutes of cooking), serve hot.