For the beef salad with core oil, first remove the skin from the onions and cut them into rings. Wash the chives and cut into rolls about 2 cm long. Thinly slice the cooked beef.
For the marinade, mix vinegar with a little water and season with salt and pepper. Slowly add oils in order, stirring vigorously throughout. Pour half of the marinade over beef and let sit for about 5 minutes.
Pour remaining marinade over onion rings, mixing gently. Pour meat into plates or bowls, top with onion rings. Garnish the beef salad with pith oil with the chive rolls.