Remove the skin from the chicken joints, except for any small pieces, such as the wings. Season the flour with salt and pepper and coat the joints.
Heat 2 teaspoons of the oil in a large frying pan and add the leek, parsley and fennel seeds. Cook over a medium heat until the leek is softened, stirring frequently. Remove from the pan with a slotted spoon and set aside.
Add the remaining oil to the pan and sauté the chicken for 6–7 minutes or until golden. Remove the chicken from the pan and set aside. Pour in the marsala and let it bubble until it is reduced to about 2 tablespoons of glaze. Pour in the stock, and return the leek mixture and dark meat chicken joints and wings to the pan (wait to add the breasts as they can overcook). Add the fennel. Cover and simmer over a low heat for 10–15 minutes, then add the breasts and continue to cook, covered, for 15 minutes or until all the chicken joints are tender. Add the peas for the last 5 minutes of cooking.
Using a slotted spoon, remove the chicken pieces and vegetables to a platter or serving bowl. Keep warm.
In a small bowl, mix the lemon juice into the egg. Slowly add about 1/3 cup (80 ml) of the hot cooking liquid to the lemon and egg mixture, stirring well, then slowly stir this mixture back into the liquid in the pan. Return the chicken and vegetables to the pan and gently warm on a very low heat so the sauce does not curdle. Season to taste. Serve garnished with parsley and lemon zest.