Preheat the oven to 325 degrees F (165 degrees C).
Layer lamb, onion, potatoes, carrot, and celery in an oven-proof pot or casserole dish. Season each layer with parsley, salt, and pepper as you go. Pour in beef stock and cover tightly.
Bake in the preheated oven until lamb is very tender, about 1 ½ to 2 hours. Divide into bowls and garnish with additional parsley.