2 quarts water
3 tablespoons salt
2 teaspoons cayenne pepper, or to taste up to 2 tablespoons
1 small red onion , thinly sliced
1 tablespoon coriander seed
1 tablespoon mustard seed
1 teaspoon celery seed
1 tablespoon dried red chile pepper flakes
5 whole cloves
5 allspice berries
3 bay leaves
2 lemons, cut in half
3 cloves garlic, finely chopped
1 (2-inch) piece fresh gingerroot , finely chopped
2 pounds fresh shrimp
2 tablespoons fresh basil, chopped
Combine the water, salt, cayenne, and onion together in a large soup pot. Bring the mixture to a boil over high heat.
Meanwhile, use a spice mill or mortar and pestle to thoroughly blend the coriander, mustard seed, celery seed, red pepper flakes, clove, allspice, and bay leaf until finely ground.
Add the spice mixture to the pot. Add the lemon halves with the garlic and ginger when the water is boiling. Simmer the mixture for about 10 minutes before adding the shrimp.
Add the shrimp, heat off and cover the pot with a tight-fitting lid. Let the shrimp steep to cook, until white throughout, about 5 minutes.
Drain the shrimp through a colander and spread them evenly on a baking tray until cool enough to handle.
Refrigerate the shrimp in an airtight container with the cooked lemon halves. Squeeze the cooked lemon halves over the shrimp and toss with the basil just before serving.