For the roast beef, wash the meat and pat dry. Remove fat and tendons. Season meat with salt and pepper. Heat 3-4 tablespoons of oil in a frying pan and fry the meat for 6-8 minutes.
Cook in the preheated oven (electric cooker: 80 °C/circulating air and gas: see manufacturer) 3 1⁄2 for 4 hours (core temperature approx. 65 °C).
For the potato salad, wash the potatoes, cover and cook in water for about 20 minutes. Quench, peel and let cool down.
Cut the potatoes into slices. Peel 2 onions and cut into fine cubes. Finely dice the bacon. Heat 5 tablespoons of oil in a pan and fry the bacon until crispy. Fry the onions for about 2 minutes.
Season with salt, pepper and 1-2 tablespoons of sugar. Deglaze with vinegar and 1⁄8 l water. Stir in broth and sweet mustard, bring to the boil and simmer for about 3 minutes. Mix with the hot marinade and let it stand for at least 30 minutes.
For the apple and onion topping, in the meantime finely dice the apple rings and let them swell in warm water for about 45 minutes. Peel onion and dice very finely. Wash the thyme, pluck off the leaves and chop finely.
Finely crumble the toast. Mix crumbs, diced onion, thyme, apple jelly, butter, mustard, coarse pepper and a little salt. Drain the apples, squeeze them and stir them into the butter mixture. Remove meat from the oven.
Preheat the oven grill. Spread the apple mixture over the meat and press it down (see picture below). Bake the roast beef under the hot grill for 10-15 minutes.
For the potato salad, wash and halve the tomatoes. Wash the lamb's lettuce and shake dry. Fold both into the potatoes. Season to taste with salt and pepper. Take the meat out of the oven, let it rest for a short time and cut it open.
Dress everything.