For the cocktail sauce: Whisk first 4 ingredients together in a small bowl to blend. Season to taste with salt. DO AHEAD: Cocktail sauce can be made 5 days ahead. Cover and chill.
For the Lemon Tarragon Vinaigrette: Combine lemon juice, shallot, tarragon, and Dijon mustard in a small bowl. Gradually whisk in oil. Season to taste with salt and pepper. Vinaigrette can be made 3 days ahead. Cover and chill.
For 20 people, buy 4 pound shrimp. For 30, buy 6 pound shrimp. Cook in batches. Place some shrimp on a platter of ice; refrigerate the rest for replenishing.
Shrimp: Levels of glutamate (40 mg/100g)
Recipe courtesy of Bonappetit.com
Photo credit: Flickr user, Pete Jelliffe
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