In a large bowl, whisk together eggs, schmaltz and seltzer.
Then add matzo meal, onions, baking powder, salt and pepper. Mix with a large spoon just until combined. Do not overmix.
The mixture will be sticky, so refrigerate batter for 30 minutes or up to 4 hours so it is not as sticky.
Bring a large pot of salted water to a boil, and then reduce to a simmer.
Shape the matzo mixture into 25 or so 1-inch balls, and place in the water. Do not overwork. I make all the balls first, and then place in the water so they cook evenly. Wetting your hands slightly helps keep them from sticking. Cover and simmer for 30-40 minutes until puffed up and cooked through.
Heat up your broth separately and then, add carrots, parsnips, celery and any other veggies you choose and chicken, and simmer covered for 10 minutes until the veggies are tender. Serve with balls!
Add salt to taste and garnish with parsley or dill.