Velvety, beautiful mache needs light partnering if it is to be appreciated. Here, a gentle topping of lemony cream enriches the baby leaves, but does not hide them.
Gently separate mache leaves at base. Separate Bibb leaves; break into small pieces. Delicately rinse both in bowl of water. Spin dry; roll in toweling; chill.
In a small bowl whisk together lemon juice, mustard, sugar, salt, and pepper. Beat in heavy cream; gradually beat in oil. Chill at least ½ hour.