Lobster tails are often sold raw and frozen in the shell, but it's less common with whole lobsters. They're ordinarily pre-cooked and then blast-frozen at the processing plant, to preserve the fresh and delicate flavor of the lobsters and make them more durable for shipping and storage. They can be thawed overnight in your refrigerator and then warmed or eaten cold, but if you're pressed for time, you can also heat them directly from their frozen state.
Place a large pot on your stove's biggest burner, and fill it with water. For standard-sized lobsters averaging about 1 1/2 pounds, allow roughly 3 quarts of water per lobster. Add 2 tablespoons of sea salt per quart, and bring the water to a full rolling boil.
Drop your frozen lobsters into the pot, taking care not to splash yourself with the boiling water. Bring the pot back to a full boil. This can take a few minutes, depending on the heat of your burner.
Remove your pot from the heat and cover it with its lid. If the lobsters are approximately 1 1/2 pounds in weight, they'll need 10 to 12 minutes to warm all the way through. Smaller 1-pound lobsters typically only need 9 to 10 minutes, while larger 2-pound specimens could take 15.
Remove a lobster from the pot with a pair of tongs. Grasp it with a clean towel, and bend it to open a gap between its body and tail. Insert an instant-read thermometer through the gap, into the thickest part of the tail. Your lobsters are ready to serve when the internal temperature reaches 160 degrees Fahrenheit.
Drain the lobsters and serve them hot with your favorite garnishes and side dishes.