The way the pros do!
Fill a deep container with enough water to cover the lobsters, adding 3/4 cup (175 mL) of salt for each gallon (4 litres) of water. Some cooks like to toss in an extra tablespoon or two of salt “for the pot.” When the water is boiling vigorously, pick up a lively lobster by the back and plunge it head first into the water. While most cooks agree that death comes instantaneously by this method of immersion, there are others who squirm at the sounds emitting from the pot. In which case, you may want to leave the area for a couple of minutes.
Cook no more than two to four lobsters at a time, so there will be room for the water to cover and boil around them. Cover the pot until the water returns to a boil, then uncover partially to allow steam to escape and prevent overflowing, and start the timing. Lobsters should be cooked on the basis of 12 minutes for the first pound (500 g), plus four minutes for each additional pound. So, a 1.5- to 2-pounder requires about 16 minutes to cook. Immediately place them in the sink and rinse with cold water to stop the cooking process, and serve warm. If cooking ahead, cool the lobsters completely in cold water and place them in refrigerator until needed.