LOBSTER ROLLS WITH LEMON VINAIGRETTE AND GARLIC BUTTER

4 (1 1/4- to 1 1/2-lb) live lobsters 3 tablespoons fresh lemon juice 1/3 cup extra-virgin olive oil 1/3 cup thinly sliced scallions 1/4 cup finely chopped peeled celery 1/4 cup celery leaves 1/4 cup chopped flat-leaf parsley 1/2 stick unsalted butter 3 garlic cloves, smashed 6 hot dog buns, preferably top-split ACCOMPANIMENT: lemon wedges

Prepare a gas grill for direct-heat cooking over medium-high heat; see “Grilling Procedure.” Plunge 2 lobsters headfirst into a large pot of salted boiling water and cook, partially covered, over medium-high heat 8 minutes (for 1 1/4-lb lobsters) to 9 minutes (for 1 1/2-lb lobsters) from time they enter water. Transfer with tongs to an ice bath and let stand until completely cooled. Return water to a boil and cook and cool remaining 2 lobsters. Remove meat from claws, joints, and tails. Save carcasses, shells, and any roe for another use (see "To Make Lobster Stock" and "To Make Lobster Oil"). Coarsely chop meat. Whisk together lemon juice, oil, and 1/2 tsp salt in a large bowl. Whisk in scallions, celery, celery leaves, and parsley, then add lobster and gently toss. Season with salt. Melt butter with garlic in a small saucepan over low heat, mashing garlic with a spoon. Brush inside of buns with garlic butter. Grill, buttered side down, until golden, about 1 minute. Fill buns with lobster.