Wash the potatoes and cook for about 20 minutes. Boil eggs hard. Quench both, peel and let them cool down. Peel and chop the onions. Boil up 1/4 l water, vinegar, onions, stock, some salt and pepper. Cut potatoes into slices and add to the marinade. Let cool off
Finely dice the cucumbers. Wash and chop the chives. Chop the eggs. Mix everything, put 2 tablespoons aside. Mix the rest with yoghurt, mayonnaise and capers. Season and stir into the potatoes. Leave to stand for at least 1 hour.
Wash, dab and season the meat. Place on the fat pan. Heat clarified butter and pour over. Roast in the hot oven (electric cooker: 225 °C/circulating air: 200 °C/gas: level 4) for approx. 30 minutes. Reduce heat to 175 °C (fan oven: 150 °C/gas: level 2). Finish roasting the meat for approx. 20 minutes. Wrap in foil and let rest for 10-15 minutes
Season the tartar sauce to taste. Slice roast beef warm or cold. Arrange everything and sprinkle with the rest of the egg-cucumber mixture. Garnish with parsley
If the roast beef is to be served cold, you can also fry it the day before. It becomes particularly tender and juicy with the low temperature method: after browning (15 min. at 250 °C) continue frying at 70 °C for approx. 4 1/2 hours. Wrap in aluminium foil and leave to cool