How to Make It
Bring a pot of water to a boil. Arrange the salmon fillets in a deep skillet in a single layer. Add the wine, celery, onion, bay leaf and peppercorns and enough of the boiling water to fully cover the salmon. Cook over moderate heat at a bare simmer until the salmon is just firm, about 10 minutes. Transfer the salmon to a platter and pat dry. Sprinkle lightly with salt.
In a heatproof bowl set over a pot of simmering water, whisk the egg yolks with the water, lemon juice, mustard, chopped tarragon and cayenne until slightly thickened, about 2 minutes. Gradually add the butter, whisking constantly until fully incorporated, about 5 minutes. If the sauce is too thick, whisk in warm water, 1 teaspoon at a time, until the sauce is just pourable. Season with salt.
Spoon the hollandaise over the salmon fillets, garnish with tarragon leaves and serve.