Wash the meat, dab dry, remove all but a small amount of fat. Cut the surface of the meat several times crosswise. Heat 1 tablespoon of oil in a large frying pan. Brown the meat in it for 7-8 minutes, remove and place on a baking tray. Mix 2 tsp. salt and pepper and 2-3 tbsp. oil. Coat the meat all around. Cook in the preheated oven (electric cooker: 100 °C/ convection oven: 75 °C/ gas: unsuitable) for 1 1/2-2 hours. Core temperature should be 56 °C. (Use meat thermometer.)
Wash the potatoes, cover and cook in plenty of boiling water for about 20 minutes
Peel and finely chop the onion. Heat the fat in a pot and fry the onion. Stun with flour, sweat briefly, add stock and cream while stirring. Bring to the boil and simmer for about 5 minutes while stirring. Season cream sauce to taste with salt, pepper and nutmeg
Drain the potatoes, rinse under cold water and peel the skin. Cut the potatoes into cubes, fold them into the sauce and place them in a wide ovenproof dish. Sprinkle with cheese
Remove the meat, cover with aluminium foil and leave to rest. Gratinate the potatoes in a preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: level 4) for 25-30 minutes. Wash and drain the tomatoes and place them in a slightly smaller ovenproof dish. Season tomatoes with salt and pepper and sprinkle with 2-3 tablespoons of oil. Add to the potatoes in the oven after about 10 minutes
Peel and finely chop the shallots and garlic. Wash herbs, shake dry, pluck leaves from the stalks and chop. Wash lemon, grate dry, finely grate peel. Halve lemon, squeeze juice. Mix herbs, garlic, shallots, lemon juice and 100 ml oil, season with salt, pepper and sugar.
Cut the meat into thin slices. Remove potatoes and tomatoes from the oven, arrange on plates with meat and herb sauce