Slow-Baked Salmon with Avruga Caviar Sauce

Preparation Put oven rack in middle position and preheat oven to 250°F. Spread butter over bottom of a 13- by 9-inch baking dish and sprinkle with 1/2 teaspoon fleur de sel. Put salmon, skin sides down, in dish and bake, uncovered, until just cooked through, 30 to 35 minutes. About 10 minutes before salmon is done, put créme fraîche in a 1- to 1 1/2-quart heavy saucepan and heat over low heat, stirring occasionally, until just melted. Transfer to a blender along with water and caviar and purée into a very smooth emulsion. Return to saucepan and keep warm, uncovered, over very low heat, stirring occasionally. Thin sauce slightly with a little additional hot water if too thick. Just before salmon is done baking, heat oil in a 12-inch skillet over moderately high heat until hot but not smoking, then add greens in 3 batches, stirring and turning with tongs until greens are slightly wilted before adding each new batch, and continue to cook, stirring, until completely wilted, 1 to 2 minutes. Push greens to one side of skillet and pour off liquid (discarding it). Divide greens among 4 plates. Top greens with salmon and season lightly with fleur de sel, then squeeze some of lime juice from wedges over salmon. Stir 1/2 teaspoon lime juice into sauce and spoon onto plates.

Preparation Put oven rack in middle position and preheat oven to 250°F. Spread butter over bottom of a 13- by 9-inch baking dish and sprinkle with 1/2 teaspoon fleur de sel. Put salmon, skin sides down, in dish and bake, uncovered, until just cooked through, 30 to 35 minutes. About 10 minutes before salmon is done, put créme fraîche in a 1- to 1 1/2-quart heavy saucepan and heat over low heat, stirring occasionally, until just melted. Transfer to a blender along with water and caviar and purée into a very smooth emulsion. Return to saucepan and keep warm, uncovered, over very low heat, stirring occasionally. Thin sauce slightly with a little additional hot water if too thick. Just before salmon is done baking, heat oil in a 12-inch skillet over moderately high heat until hot but not smoking, then add greens in 3 batches, stirring and turning with tongs until greens are slightly wilted before adding each new batch, and continue to cook, stirring, until completely wilted, 1 to 2 minutes. Push greens to one side of skillet and pour off liquid (discarding it). Divide greens among 4 plates. Top greens with salmon and season lightly with fleur de sel, then squeeze some of lime juice from wedges over salmon. Stir 1/2 teaspoon lime juice into sauce and spoon onto plates.