4 (1 1/2-lb) live lobsters or 1 1/2 lb cooked fresh lobster meat
1 lb small red potatoes
3 ears corn

For vinaigrette
2 1/2 tablespoons fresh lemon juice
1 1/2 to 2 tablespoons chopped fresh tarragon
1/2 teaspoon Dijon mustard
1/2 teaspoon salt
1/4 cup extra-virgin olive oil

2 cups grape or cherry tomatoes, halved
1 cup coarsely chopped fris�e (French curly endive)
1/3 cup sliced scallion

Prepare lobster, potatoes, and corn:
Plunge 2 live lobsters headfirst into an 8-quart pot of boiling salted water. Cover and cook lobsters over moderately high heat 9 minutes from time they enter water, then transfer with tongs to sink to cool. Return water to a boil and cook remaining 2 lobsters in same manner. Leave water boiling in pot.
Simmer potatoes in lobster cooking water until just tender, 15 to 20 minutes. Transfer with a slotted spoon to a colander, reserving boiling water in pot.

Boil corn in same water until crisp-tender, about 3 minutes, then drain.

When lobsters are cool, remove meat from claws, joints, and tails, reserving shells for another use.

Cut meat into 1-inch pieces. Cut potatoes into 3/4-inch pieces, and cut corn from cobs.

Make vinaigrette:
Whisk together lemon juice, tarragon, mustard, and salt until combined, then add oil in a thin stream, whisking.

Assemble salad:
Just before serving, toss together lobster meat, potatoes, corn, vinaigrette, tomatoes, fris�e, and scallion in a large bowl and season with salt and pepper.

Cooks' note:
� Lobster may be cooked 1 day ahead

Makes 4 servings.