For the matzo balls: Combine the matzo meal, salt, pepper and onion powder in a large bowl. Combine the eggs and schmaltz in a second large bowl. Very gently mix the wet ingredients into the dry ingredients. Cover and refrigerate for one hour.
Bring a large pot of water to boil and season well with salt.
Using wet hands, form the matzo mixture into 1 1/2-ounce balls. (Be gentle: overmixing can result in tough, hard dumplings.)
Add the dumplings to the pot of water and cook until cooked all the way through, about 45 minutes. The dumplings can be held in warm water until ready to serve.
For the soup: Sweat the onions, carrots and celery in a large soup pot with the schmaltz until soft and translucent, about 10 minutes. Add the chicken stock and bay leaves and bring to a boil. Lower the heat and simmer until the vegetables are very tender, 20 minutes. Skim any foam or bits of food that have risen to the top. Discard the bay leaves. Add salt and pepper to taste.
Just before serving, add the noodles and chicken and heat through. Place 2 matzo balls in each bowl and add the soup.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.