Preparation

• Let the salmon sit at room temperature for 30 minutes while you make the poaching liquid.
• To make the poaching liquid, combine 3 cups of the wine, the carrot, onion, lemon, 8 parsley sprigs, 5 thyme sprigs, the peppercorns, bay leaves, 2 tsp. salt, and 3 cups water in an 11- to 12-inch skillet or sauté pan; bring to a boil. Cover the pan with a tight-fitting lid; if the lid isn’t snug, cover with foil and then the lid. Turn the heat down and simmer for 10 minutes. Turn the heat off and let stand until ready to use.
• To make the beurre blanc, combine the remaining 1 cup white wine, the citrus juices, shallot, and the remaining sprigs of parsley and thyme in a 2-quart saucepan. Boil until reduced to about 1/4 cup, about 12 minutes.
• Strain the mixture through a fine-mesh sieve into a small bowl, pressing on and then discarding the solids; rinse out the saucepan. Return the liquid to the saucepan and heat over low heat until hot, about 1 minute. Gradually whisk in the cold butter a few pieces at a time until the sauce is creamy and emulsified. Remove from the heat. Stir in the chopped parsley, season to taste with salt and pepper, cover the pan, and keep the sauce in a warm place or transfer it to a small thermos.
• To poach the fish, return the poaching liquid to a simmer and then turn the heat down to medium low. Remove and discard the herb sprigs. Gently slide the salmon into the liquid, which should come at least 3/4 of the way up the sides of the steaks; add hot water if it doesn’t. Quickly ladle some of the poaching liquid over the fish, tightly cover the skillet, and cook for 1 minute.
• 把锅from the heat and let sit, covered, until an instant-read thermometer inserted into the thickest part of the fish registers 120°F for medium rare or 125°F for medium, 7 to 10 minutes
• Using a slotted spatula, transfer the salmon to a paper-towel-lined platter or plates; let rest uncovered for 5 minutes. (The salmon will continue cooking as it rests.) Discard the paper towels and serve the fish with the beurre blanc.