Ingredient:

• 2 tablespoons butter
• 1 large leek, cleaned and thinly sliced
• ½ cup sliced shallots
• ½ teaspoon salt, and more to taste
• ¾ cup white wine
• 1 ¼ cups chicken broth
• 1 pound baby red potatoes, trimmed
• ½ cup thinly sliced fennel bulb
• 1 pinch cayenne pepper, or more to taste
• freshly ground black pepper to taste
• ½ cup heavy cream
• 1 pound boneless rockfish fillets, cut into 1-inch pieces
• 1 tablespoon chopped fresh tarragon