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For sauce: Combine first 3 ingredients in saucepan. Boil until liquid is reduced to 3 tablespoons, stirring occasionally, about 20 minutes. Add cream and boil until sauce is reduced to 1 1/2 cups, about 15 minutes. Strain sauce. Season with salt and pepper. Can be made 1 day ahead. Cover and chill.
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For Fish: Preheat oven to 350. Mix first 3 ingredients in medium bowl. Add butter and mix with fingertips to form coarse crumbs. heat 2 tablespoons oil in heavy large skillet over medium high heat. Add fish and cook until golden brown, about 3 minutes per side. Using spatula, transfer fish to baking sheet; cool. Sprinkle breadcrumb mixture over fish; press gently with fingertips to adhere. Bake fish until firm to touch, about 10 minute.
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Meanwhile, heat remaining 1 tablespoon oil in heavy large skillet over high heat. Add spinach and cook until wilted, stirring frequently.
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Preheat broiler. Transfer fish to broiler; broil until crust browns, about 1 minute. Divide spinach among plates. Top with fish. Bring sauce to simmer. Mix in dill and lemon juice and zest. Season with salt and pepper. Ladle sauce around fish.