In a bowl stir together creme fraiche, zests, juices, tarragon, and salt and pepper, to taste. Chill sauce, covered, 1 hour to blend flavors.
Cut 3 inches of cucumber crosswise into very thin slices and reserve. Reserve 8 endive leaves for garnish and cut remaining cucumber and endive into 2-inch long matchsticks.
Just before serving, coarsely chop lobster and in another bowl stir together with 3/4 cup sauce. Stir matchstick vegetables into remaining sauce.
Line 4 Martini glasses with reserved cucumber slices. Divide matchstick vegetable mixture among glasses and top with lobster salad. Cut reserved endive lengthwise into 1/4-inch thick strips. Garnish salad with endive, mesclun, and chives.
Recipe courtesy of Gourmet Magazine from The Library, The Regency Hotel, New York City