There are no shortcuts in this classic Passover recipe: The soup, perfect for lunch or dinner, calls for homemade broth, chicken feet, and hours of simmering. But the finished soup, starring one big, fluffy dumpling, is a straight shot to the soul.
Beat eggs in a large bowl. Stir in matzo meal, seltzer, schmaltz, ginger, celery seed, herbs, 1 teaspoon salt, and 1/4 teaspoon pepper. Stir until combined (mixture will be loose).
Cover and refrigerate until mixture stiffens slightly, at least 30 minutes and up to 1 day. Place 2 cups broth in a wide pot. Add water to fill pot to 2 1/2 inches. Bring to a boil; season with 1 tablespoon salt. With dampened hands (to prevent sticking), divide chilled matzo mixture into 6 equal portions. Form each into a sphere.
Gently place balls in pot, one at a time. Cover and reduce heat to low to maintain a simmer (do not let boil). Cook, turning them a few times, until puffed and cooked through to center, 1 hour to 1 hour, 15 minutes.
Meanwhile, bring remaining 10 cups broth and carrots to a boil in a separate pot. Reduce heat to medium-low; simmer until carrots are tender, 12 to 15 minutes. Season with salt. Transfer matzo balls to serving bowls. Divide broth and carrots evenly among them; top with more herbs. Serve immediately.