Prepare the vinaigrette by mixing sherry vinegar, walnut oil, peanut oil, chopped chervil, salt, pepper.
Peel and wash the sweet potato in several waters, drain, spin dry.
Cook the ray in court-bouillon or, failing that, in salted water, cooking according to thickness, then remove the skin on each side and lift the flesh, preventing it from falling apart.
Mix the lamb's lettuce with half the vinaigrette and serve on a plate.
Season the skate and arrange it on the salad.
Sprinkle with chopped chervil. As an indication, it is difficult to indicate the cooking time of the skate. For a thick ray count 20 minutes, for small fins half will be enough, in any case check that the flesh detaches well from the bone.
