This elegant fennel gratin is our adaptation of a recipe from “David Tanis Market Cooking” by David Tanis. Fresh fennel has a celery-like crispness when raw but cooking renders it supple and tender while also turning its flavor sweet and mellow. We agree with Tanis that for optimal texture, fennel benefits from a quick blanch prior to baking to ensure the slices fully soften, but be sure to dry them well after draining to remove excess water that otherwise would result in sogginess. Crushed fennel seeds amplify the licorice notes of the fresh fennel; either pulse the seeds in an electric spice grinder or bash them in a mortar with a pestle.