Take the chicken out of the fridge and leave to come to room temperature. Scrub the jerusalem artichokes in cold water with wire wool or similar, then halve or quarter them, depending on their size; discard any skinny or gnarled ends (don’t worry about bits of skin in the nooks and crannies, because you’re going to simmer them).
Put the artichokes in a pan of salted water, add the lemon juice, bring to a boil, then simmer for 15-20 minutes, until they are tender to the point of a knife.
Meanwhile, prep the chicken. Generously season the thighs all over. Put a 28-32cm wide shallow ovenproof pan or casserole on a medium heat, add a splash of the oil and the pancetta, then lay in the chicken thighs skin side down.
Run your hand down the rosemary sprigs to strip the leaves into the pan, then cut the head of garlic in half, prise apart the cloves (reserve one clove for the salad below) and drop into the pan; discard any skins that fall off. Leave to cook for eight to 10 minutes, until the chicken starts to brown.
Heat the oven to 200C (180C fan)/390F/gas 6. Lift the chicken thighs out of the pan, add the onion and artichokes, season generously and stir. Pour over the remaining olive oil and the vinegar, and roast the veg for 20 minutes.
Return the chicken thighs to the pan on top of the vegetables and cook for a further 35-40 minutes, until the chicken is brown and crisp and the vegetables caramelised and delicious. Serve with a salad.
