Paupiettes de Sole a la Vapeur

Name: Paupiettes de Sole a la Vapeur
Ingredients: 1/2 small leek (white and pale green parts only); a 3inch piece carrot; a 3inch piece celery rib; 3 medium garlic cloves; 7 cups cold water; 1 cup plus 2 tablespoons red wine vinegar; 1 fresh thyme sprig; 2 bay leaves (not the stronger California variety); 1 1/2 teaspoons white peppercorns; 1 teaspoon fine sea salt; 4 fish fillets of sole or any other white fleshed fish, 3/8-inch thick, trimmed to about 6 inches in length; 4 salmon strips, 1 by 6 inches; 3 tablespoons unsalted butter or oil, at room temperature; 1 teaspoon salt; 1/4 teaspoon white pepper; 1 tablespoon finely chopped parsley