In Provence, fennel grows wild along the roadside and easily in the garden. Since it is one of Patricia Wells' favorite vegetables, no one needs coax her to prepare this dish. Anything that comes bubbling from the oven with a nice coating of cheese wins her appetite! Much of the work can be done in advance. The fennel is lightly browned in olive oil, then braised in a touch of broth. The drained fennel is gratin?ed at the last minute under the broiler.