Set large pot of water on stovetop and turn on the heat. Squeeze in the juice from all four lemon halves and add them as well along with the bay leaves, celery seed, salt, and other spices if you have them (if not, no worries).
Bring stockpot of goodies just barely to a boil and let simmer 5 minutes to infuse the liquid. Get a bowl of ice water ready, you will put the shrimp in here immediately after cooking. Lower the heat under the stockpot until water stops simmering.
Add shrimp and move them around in the hot water to evenly distribute the heat. The shrimp are done when they have turned opaque and pink, about 3 minutes. Keep the water hot, but not boiling during this poaching time.
Using a slotted spoon, transfer cooked shrimp to the ice bath to stop the cooking. After a minute or so, transfer shrimp to a plate and chill until ready to serve.