In a large pot bring the chicken stock to a brisk simmer. Add the whole chicken and enough water to completely cover the chicken. Reduce the heat and gently simmer the chicken, partially covered for 2 1/2 hours. Remove the chicken from the stock and let cool. Discard the skin and the bones and shred the chicken meat. Set aside. Strain the broth through a fine mesh sieve. Quickly cool the stock and either refrigerate or freeze the stock until ready to use. Once you are ready to use the stock skim the fat from the top of the stock and reserve it to saute the vegetables for the soup.

In a medium size mixing bowl combine the egg yolks with the schmaltz and the seltzer water and mix well. In a small bowl combine the matzoh meal, salt, pepper and baking powder mix well. Add the matzoh meal mixture to the egg yolk mixture and mix well. Add the chives.

In a separate bowl, beat the egg whites to a soft peak. Fold the egg whites and the matzoh mixture together. The mixture should resemble wet sand. Refrigerate for at least one hour and up to overnight.

Line a baking sheet with plastic wrap or parchment paper. Using a spoon or an ice cream scooper, scoop 1 1/2 tablespoon portions of the mixture onto the baking sheet. Wet your hands with a little water and then roll each scoop into a ball. Return the matzoh balls to the refrigerator for at least 30 minutes.

In a large soup pot, over medium heat, add 2 tablespoons of the reserved fat. When melted, add the onions, carrots, parsnips, and celery and cook, stirring, until the vegetables are wilted, 2 to 3 minutes. Add the chicken broth to the pot, and bring the soup to a simmer. Add the matzoh balls to the broth, cover and gently simmer until the matzoh balls until they are plump and cooked through, about 25 minutes. Stir in the shredded chicken and cook just until the meat is warmed through, about 2 minutes.

Season the soup with salt and pepper and garnish with the chiffonade of parsley.

Serve immediately.