Cos Lettuce Salad

Remove all the green leaves until the yellow ones are reached; wipe each leaf well, and split them lengthwise, then cut into two-inch long pieces, continuing as far as the heart; split it in four; place in a salad bowl and season the salad with chervil, tarragon, all finely cut, egg-yolks (one egg for two persons) and dilute with eight spoonfuls of oil and two of vinegar; add salt, pepper and green mustard; mix well when ready to serve. The egg-yolks may be suppressed.