Cut off the upper layer of fat from the roast beef (some fat should remain). Season with salt and pepper. Heat the lard in a flat roasting pan. Fry the meat on all sides over a high heat for 6-8 minutes. Place the meat in the preheated oven (electric cooker: 80 °C/ convection oven and gas: see manufacturer) with the fat layer facing upwards and roast for approx. 4 1/2 hours.
For the crust, roughly crush peppercorns and mustard in a mortar. Wash thyme, shake dry and pluck off leaves. Mix everything and after about 1 hour roasting time spread it on the roast beef
For the potato salad, wash the potatoes and cook in boiling water for about 20 minutes. Drain, quench, peel and let cool off
Onions peel and chop finely. Heat the oil in a wide saucepan. Fry the onions in it until transparent. Add 200 ml water and vinegar, bring to the boil. Stir in stock and simmer for about 2 minutes. Season with salt and pepper. Cut potatoes in slices directly into it. Mix everything loosely. Leave to stand for 1 hour
Peel the cucumber and slice or slice it thinly. Clean, wash and dry lamb's lettuce. Shortly before serving, add the cucumber and lamb's lettuce to the potatoes. Season again with salt and pepper. Remove the roast beef and let it rest for a short time. Then cut into thin slices and serve with the potato salad. Remoulade tastes good with it
waiting time approx. 4 1/2 hours