Preheat the oven to 300?F.
In a medium saucepan, combine the Shrimp Stock, white wine, grapefruit juice, bay leaf, garlic, peppercorns, thyme, tarragon, and shallots. Bring to a boil over medium-high heat, then reduce the heat to a simmer. Simmer the infusion for 15 minutes, then remove from the heat.
Take two pieces of aluminum foil, 2 feet long, and lay them, overlapping, side by side lengthwise. Lay the salmon perpendicular to the seam, and pick up the salmon by grabbing both ends of foil right at the point where they meet. Place the salmon in a roasting pan (we used one 11.5 x 15 inches) or another large baking dish with high sides that is just long enough to hold the side of salmon. Season the salmon with the kosher salt and white pepper and pour the hot poaching liquid over the top of the salmon. The liquid should come at least halfway up the side of the salmon. Cover the roasting pan with aluminum foil and place in the oven. Cook the salmon for 18 minutes, remove from the oven, and remove the aluminum foil cover. Using the two sheets of aluminum foil underneath the salmon, carefully grasp the sheets on both sides where the edges overlap in order to lift the salmon out of the poaching liquid. Lay the salmon on a large platter, and strain the poaching liquid into a saucepan and place over medium-high heat. Bring the liquid to a boil, reduce the heat to medium, and continue to boil and reduce the liquid until you have 1 cup left, 20 to 25 minutes. Remove from the heat and reserve the liquid for making the sauce.
Makes 6 to 8 servings
FOR THE SAUCE:
Set a 1-quart saucepan over medium heat. Add 1 tablespoon of the butter to the pan, and when it melts and turns frothy, add the shallots and garlic to the pan. Stir continuously for 1 minute, then deglaze with the white wine. When the wine has nearly completely evaporated, add the reduced poaching liquid, heavy cream, and black pepper. In a small mixing bowl, combine the remaining 2 tablespoons of butter with the flour, and mash together to form a paste; this is also known as a beurre maniČ. Once the saucepan comes to a boil, add the beurre maniČ and whisk vigorously to incorporate. Cook the sauce for 20 minutes, or until any floury taste is gone. Taste and reseason the sauce if necessary. Remove the sauce from the stovetop and let cool before serving with the salmon. The salmon and sauce may be served warm, at room temperature, or even chilled.