The aniselike flavor of fennel makes it a perfect partner for poached salmon or broiled swordfish.
1. Trim the fennel, reserving the feathery leaves. Coarsely chop the leaves and measure out 1 tablespoon. Set aside. Cut the heads in half lengthwise and drop into a large pot of boiling, salted water. Cook, uncovered, at a gentle bubble for 20 to 25 minutes or until tender when pierced. Remove with a slotted spoon and drain on absorbent paper. Pat dry.
2. Meanwhile, whisk together the lemon juice, mustard, salt, and cayenne. Whisk in the oil, then stir in the shallot and fennel leaves. Brush over the surface of the fennel and arrange the halves, cut side up, in a shallow broiling pan. Slide under the broiler and cook, basting frequently, for 10 to 12 minutes or until the surface looks slightly golden and bubbly. Serve hot or at room temperature, spooning on any remaining vinaigrette.