1. Heat the oil in a large, wide casserole that comes with a lid (and can be taken to the table) and add the pancetta cubes (or lardons or bacon), cooking them until they begin to give off their juices and start to colour.
2. Add the chicken thighs (skin-side down if yours have skin), tossing the pancetta cubes on top of the meat (to stop the pancetta burning and to make space) as you put the poultry in the pan, and cook for about 5 minutes over a medium heat.
3. Turn the thighs over and tip in the prepared leek, celery and garlic. Season with the dried tarragon, salt and pepper, then stir everything around a bit, letting it cook for another 5 minutes.
4. Pour in the cider, then sprinkle in the frozen peas. Bring the pan to a boil then cover, turn down to a very gentle heat and cook for 40 minutes. Do check after 30, though, to see if the chicken is cooked through, and if you are disobeying me and going boneless, then 20 minutes should do it.
5. Remove the lid, stir in the mustard, and then toss the shredded lettuce over the chicken, letting it wilt in the hot sauce for a couple of minutes.
6. Scatter the chopped tarragon over the casserole and take the steamily fragrant pot to the table with quiet pride.

(Nigella Lawson, 2013)