Stock: Place the stock ingredients in a soup kettle and bring to a simmer over moderate heat. Partially cover the kettle and poach the chicken for 30 to 40 minutes, or until the thigh juices run clear when pierced with a kitchen fork. Remove and discard the vegetables from the soup and let the chicken cool in the stock.

When the stock is cool, remove the poached chicken and refrigerate the stock and the chicken separately. Reserve the chicken for sandwiches and chicken salads.

Matzo balls: In a bowl, lightly beat the eggs and combine with the seltzer. Add the chicken fat and blend. Gradually add the matzo meal, stirring until the mixture is spongy and lightly thickened. Add the parsley and seasonings and blend. Cover and refrigerate for at least 30 minutes.

Remove the mixture and the stock from the refrigerator 30 minutes before preparing the soup.

Skim the stock of all fat and bring to a simmer over low heat. Shape the matzo mixture into 1-inch balls, wetting your hands in cold water from time to time to prevent sticking. Increase the heat to produce a gentle boil and add the matzo balls to the soup. Partially cover the kettle and poach the matzo balls for 20 to 25 minutes, until cooked through. Test one to be sure it is cooked in the center.

Ladle 2 matzo balls and broth into each heated bowl and sprinkle with the additional parsley.