In a mixing bowl, combine matzo meal, beaten eggs, melted chicken fat, water, salt, and black pepper. Mix well and refrigerate for 30 minutes.
Bring a large pot of salted water to a boil. Wet your hands and form the matzo mixture into balls about the size of a walnut. Drop them into the boiling water, reduce heat, and simmer for 30 minutes.
In another large pot, bring chicken broth to a boil. Add carrots, celery, onion, salt, and black pepper. Reduce heat and simmer for 20 minutes.
Transfer the cooked matzo balls to the soup and simmer for another 10 minutes. Serve hot.