Preheat the roast beef oven (electric cooker: 80 °C/circulating air and gas: see manufacturer). Wash meat and pat dry. Cut off the upper layer of fat (some fat should remain). Season with salt and pepper. Heat lard in a flat roasting pan. Fry the meat in it at high heat for 6-8 minutes. Put the meat in the oven with the fat layer up and roast it for about 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 boil them 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 4 1/2 hours