Place the court-bouillon ingredients (water, white
wine vinegar,
olive oil,
parsley,
onion cut into 3-mm thick slices, coarse
salt, peppercorn) in a high-sided frying pan and bring to a boil. Reduce heat, cover, and simmer for 10 minutes. Carefully add the skate pieces, cover, simmer until cooked — about 4 minutes.