Preheat the oven to 180°C/160°C Fan/350°F.

Untruss the chicken, if it comes trussed, and remove all the string.

Prepare the vegetables: peel and cut the carrots into batons; cut the trimmed leeks into smallish rounds, approx. 1.5-2.5cm / ¾-1 inch.

Heat the oil in a large heavy-based casserole/ Dutch oven with a tightly fitting lid.

Place the chicken in the hot oil breast side down to colour the skin; do this over high heat for about 3 minutes, until the skin is richly golden.

Turn the chicken the right way up.

Turn down the heat, or take the pan off the heat completely, and add the lemon zest and minced garlic.

Scatter in the prepared vegetables around the chicken, followed by the salt, chilli flakes (if using) and dried tarragon.

Measure 1.5 litres/6¼ cups of cold water into a measuring jug.

Pour 1.25 litres / 5 cups of cold water into the chicken pot at first, and then, gradually, pour in the remaining water until the liquid comes up about two thirds of the leg of the chicken, leaving the golden breast clearly untouched by a small margin.

Now add the lemon juice.

Turn up the heat and bring the pot to a boil, leaving it uncovered.

Once boiling clamp on the lid and put into the preheated oven for 1 hour 15 minutes.

Take the pot out of the oven and stir in the orzo, around the edges of the chicken, and then put the lid on again, and put the casserole back in the oven for another 15 minutes.

Take out of the oven and remove the lid, then let it stand for 15 minutes, giving the orzo a bit of a stir to loosen any that has stuck to the bottom of the pan.

Stir in 4 tablespoons of the freshly chopped parsley, and then sprinkle over the remaining 2 tablespoons.

To serve, put a small dish by the casserole, then strip off the meat from the chicken, removing the skin and bones to the dish.

Stir the meat and orzo again before serving, adding more parsley as you do so.