Heat the oil in a large wide stove top to oven casserole with a lid over medium heat.

Add the leeks and cook, uncovered, for a moment or two.

Toss in the pancetta, lardons or bacon and continue to cook until the meat picks up a bit of colour.

Add the chicken breasts to the pan, nesting them in amongst the pancetta and leeks and cook for about 5 minutes.

Turn the chicken over and cook for about five minutes more.

Add the cider, garlic, dried tarragon, salt and pepper.

Bring the liquid to a boil, then turn back to a simmer over low heat.

Put the lid on the pan and cook for about 15 minutes.

Stir in the mustard and the peas and cook for 5 to 10 minutes more.

When the chicken is cooked (165°F internal temperature with no pink remaining inside), toss the shredded lettuce over the chicken (it should wilt a little) and sprinkle with the chopped fresh tarragon.

Serve over mashed potatoes, crushed new potatoes or rice with crusty french bread to mop up the juices.