How to cook frozen lobster tails:
Since lobster tails are usually frozen uncooked, you must either boil or broil them before serving (they should be completely thawed before cooking).
Boiling lobster tails:
In a large kettle, bring to boiling enough water to cover lobster tails; add 1 tablespoon salt for each quart water. Plunge thawed tails into water; when boiling resumes, cover kettle and simmer about 5 minutes for 4-ounce tails; add 1 minute for each additional ounce. Remove and plunge into cold water to stop cooking; drain. Serve hot, with melted butter or margarine; or let cool, chill, and serve cold or use in salads and other cold dishes.
Broiling lobster tails:
Using kitchen scissors, cut along inner edges of soft undershell of thawed lobster tails, clipping off the many fins along outer edges. Peel back soft undershell and discard. Bend overshell back, cracking some of the joints to prevent curling. Arrange on broiler pan, shell side up, and broil, about 5 inches from heat, for 4 minutes. (If lobster tails are large, split them lengthwise into 2 servings each.) Turn over and spread meat with whipped lemon butter or brush generously with melted butter or margarine; broil, meat side up, about 5 minutes longer. Serve immediately.