Place the shrimp in a large (8-inch-diameter × 5-inch-high) saucepan and add 8 cups of cold water, the Pernod, and 1 tablespoon salt. Turn the heat to medium high and cook the shrimp uncovered, stirring occasionally, for 8 to 10 minutes, until just firm and pink. Drain in a colander.
Place half the shrimp in a large bowl. Cut the rest of the shrimp sideways through the back with a sharp paring knife and add them to the bowl as well. Allow to cool for 15 minutes. Stir in the lemon juice, 2 teaspoons salt, and 1 teaspoon pepper. Add the celery, scallions, tarragon, and mayonnaise, and combine. Cover and refrigerate for at least 2 hours for the flavors to meld.
Transfer the salad to a serving bowl, sprinkle with extra tarragon and salt, and taste for seasonings. Serve cold or at room temperature.
This recipe has been updated and may differ from what was originally published or broadcast.