Brown the lamb: Heat olive oil or butter in a large pot or Dutch oven over medium- high heat. Season the lamb with salt and pepper, then brown it on all sides, about 4-5 minutes per batch. Remove and set aside.

Sauté the vegetables: In the same pot, add the chopped onion, garlic, carrots, and celery. Cook for 5-7 minutes until softened.

Simmer the stew: Add the tomato paste and stir for 1 minute. Pour in the broth, and return the browned lamb to the pot. Add the turnips, thyme, rosemary, and bay leaves. Bring the stew to a simmer, then reduce the heat to low, cover, and cook for 1.5 to 2 hours, or until the lamb is tender.

Prepare the cauliflower mash: While the stew is simmering, steam or boil the cauliflower florets until tender, about 10-12 minutes. Drain well, then mash or blend the cauliflower with butter and heavy cream until smooth. Season with salt and pepper.

Serve: Remove the bay leaves from the stew. Serve the lamb stew hot, ladled over a generous portion of cauliflower mash. Garnish with fresh parsley or chives.