Season the lamb: Pat the lamb dry. Season with 1.5 teaspoons salt and 1 teaspoon black pepper.
Dry meat browns better and gives you more flavor.
Brown in batches: Heat oil in a heavy pot or Dutch oven over medium-high. Sear the lamb in batches until well browned on all sides, 6–8 minutes total per batch. Don’t crowd the pot.
Transfer browned lamb to a bowl.
Build the base: Reduce heat to medium. Add onion and a pinch of salt. Cook 3–4 minutes, scraping up browned bits.
Add garlic and cook 30 seconds until fragrant.
Deglaze: Stir in tomato paste and cook 1 minute. Pour in red wine (if using) and simmer 1–2 minutes, scraping the pot. Add broth, rosemary, thyme, bay leaf, and coconut aminos.
Simmer the lamb: Return lamb to the pot with any juices.
Bring to a gentle simmer, cover, and cook on low for 60 minutes, stirring occasionally.
Add veggies: Stir in turnip, celery root, mushrooms, and celery. Simmer covered another 25–35 minutes, until lamb and veggies are fork-tender.
Finish and balance: Remove the bay leaf. Stir in butter or ghee and vinegar.
Taste and adjust salt and pepper. The vinegar brightens the stew without adding sugar.
Rest and serve: Let the stew sit 5–10 minutes. Garnish with parsley.
Serve as is, or over cauliflower mash or sautéed greens.