Fish Fillets in Red Wine and Cocoa Sauce from The Cooking of South West France by Paula Wolfert

Ingredients

• 1½ cups Fish Fumet, made with red wine and reduced to ¼ cup glaze
• 2 tablespoons minced fresh chives
• Coarse sea salt and freshly ground pepper
• 1 teaspoon red wine vinegar
• 4 leeks (white part and ½ inch of pale green), well washed and thinly sliced crosswise
• ¼ cup heavy cream
• 1 pound boneless fish fillets, such as trout, bass, or mullet
• 1 teaspoon unsweetened cocoa dissolved in 1½ teaspoons water
• 2 tablespoons minced shallots
• 1½ cups full-bodied red wine (see Notes)
• 1½ cups unsalted chicken stock (storebought or homemade), boiled until reduced to ½ cup
• 8 tablespoons (1 stick) unsalted butter