Bring a 6-quart pot of highly salted water to boil over high heat. Add the shrimp to the boiling water and simmer until they are cooked through, 3 to 4 minutes. With a slotted spoon or strainer, transfer the shrimp to a bowl of ice water to stop the cooking. Once cooled, drain, pat dry and reserve.
Puree the creme fraiche, tarragon, scallions, zest and lemon juice in food processor until smooth. Season with salt and pepper. Transfer to a bowl and serve with the reserved shrimp.
BYOC: For a little extra depth of flavor, try adding an anchovy fillet to the puree... trust me, it's great!