Squeeze one lemon, wash the other, dry it and cut into thin slices. Peel the garlic and press it in the garlic press. Pluck the rosemary from the stems. Mix lemon juice with 5 tablespoons of oil, garlic, thyme and rosemary. Brush the meat with it and marinate overnight in a plastic bag.
Peel, wash and halve the potatoes. Peel and halve the shallots. Dab the lamb, season with salt, pepper and fry in 2 tablespoons of oil in the roaster and then take it out again.
Put 2 tablespoons of oil with the potatoes and shallots in a roasting pan, season with salt and pepper. Braise everything in the oven at 200 degrees for 20 minutes.
Turn the temperature back to 150 degrees. Add the lemon slices and the lamb to the vegetables and stew everything together for another 50 minutes. Douse with broth every now and then.
Wash, dry and cut the tomatoes crosswise at the top. Then stew them in the roaster 10 minutes before the end of the cooking time.
Then remove the meat from the bone, cut into slices, arrange on plates with the potatoes and tomatoes and garnish with rosemary.