(Optional) If you did not buy deveined shrimp, devein all of the shrimp. Save the shells.
In a large pot, combine shrimp shells, 2 quarts of water, and 3 tablespoons of salt. Bring to a boil over high heat, reduce heat to low, and simmer for 20 minutes. Remove pot from heat and steep until cool.
(Optional) If you don't have the shells or want to save time you can replace the above poaching liquid with 2 quarts of Seafood Stock. This will save approximately 45 minutes.
Strain shrimp broth into another large pot, and bring to a boil over high heat. Add wine, peppercorns, coriander seeds, bay leaves, parsley, tarragon, and halved lemons.
Add shrimp and remove pot from heat. Steep shrimp until they are white, approximately 2 to 3 minutes.
Fill a large bowl with water, ice, and the remaining 2 tablespoons of salt. Transfer shrimp to the bowl. Let shrimp cool for 3 minutes, then drain well.
Refrigerate shrimp with a bag of ice until ready to serve.