Step 1

Whisk eggs, ¼ cup oil, ¼ cup chives, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, 1 tsp. pepper, and ¼ cup water in a medium bowl to combine. Add matzo meal and mix until no dry spots remain. Mixture will be loose. Cover and chill at least 30 minutes and up to 3 hours.

Step 2

Heat ¼ cup oil in a large Dutch oven or other heavy pot over medium. Add cabbage, onion, garlic, and 1½ tsp. pepper and cook, tossing (tongs help here!) until coated in oil and starting to wilt. Reduce heat to low, cover pot, and cook, stirring every 10–15 minutes, until cabbage is dark and starting to stick to pot, 45–60 minutes. (If cabbage is starting to stick too much before it’s done, add 1–2 Tbsp. water and scrape up brown bits stuck to bottom of pot.) Scoop out about ½ cup cabbage and set aside.

Step 3

Meanwhile, working with damp hands, divide matzo mixture into 20 pieces and roll each into about a ½"-diameter ball. Bring a large pot of salted water to a boil. Gently drop in matzo balls and reduce heat so water is at a simmer. Cover pot and cook until matzo balls puff, rise to the surface, and are tender throughout (cut one open to check), 15–20 minutes. Using a slotted spoon, transfer to a large plate or rimmed baking sheet.

Step 4

Mix leeks, potatoes, and 1½ tsp. Diamond Crystal or 1 tsp. Morton kosher salt into cabbage mixture and add 6 cups water. Increase heat to high and bring to a boil. Reduce heat and simmer gently, adding any matzo balls you will be eating in the final 5 minutes, until potatoes are tender 10–12 minutes. (Any matzo balls that you’re not serving should be stored and reheated separately.) Remove from heat and stir in ½ cup parsley and 1 tsp. lemon juice. Taste soup and season with more salt and add remaining 1 tsp. lemon juice if needed.

Step 5

Ladle soup into bowls, then top with more chives and parsley and reserved cabbage. Season with pepper and drizzle with a little oil.Do ahead: Matzo balls can be cooked in water 5 days ahead. Cover and chill. Reheat in soup just before serving.