For Schmaltz: Season chicken wings with salt and place them in a single layer in a large ovenproof dutch oven (6-8 qt). Roast for 45 minutes or until the fat has rendered (about ¼ cup) at 450°F. Pour the schmaltz into a bowl to cool.
Make broth: Transfer the chicken wings and onion halves to a pot. Add 6 cups of water. Simmer the broth slowly at low heat for 4-6 hours on the stove, or 30 minutes at high pressure in an instant pot, or 8 hours at low heat in a crock pot. Strain the broth and set aside.
Make Matzo balls: Gently mix all matzo balls ingredients in a bowl. Do not overmix.Cover and refrigerate for 30 minutes or up to 24 hours. With wet hands, shape the mixture into balls before cooking.
In a large pot, add broth, diced carrots, celery, and extra water if necessary. Season with salt/pepper. Bring to a boil over medium-high heat.
Gently drop matzo balls into the broth. Cover the pot, simmer on low heat for about 30-40 minutes for al dente, or longer for lighter texture. Serve with chopped parsley.
If you don't have time to make your own Schmaltz, you can substitute it with vegetable oil. Also, you can skip steps #1 and #2 by using a pre-made broth (about 6-8 cups) to speed up the cooking process.