Cut a lemon in half lengthwise and then in half again lengthwise, to make four wedges. Trim some of the pulp in an even line so that when you turn the wedge over, skin side up, it will lie flat. On the skin side, cut out a deep wedge from the center of the lemon along its length. Use the trench as a container for ikura, salmon roe, or any other ingredient that is attractive and will benefit from contact with the lemon juice in the trench (crab meat? caviar?).
