Lamb and Sorrel Soup from Soup: A Way of Life by Barbara Kafka

Ingredients

• 1 pound (450 g) lamb shoulder, trimmed of excess fat and cut into ¾-inch (1.5-cm) cubes, or 2 cups cubed leftover cooked lamb
• Freshly ground black pepper, to taste
• 6 cups (1.5 l) Lamb Stock
• 1 pound (450 g) firm potatoes, peeled and cut into ½-inch (1-cm) dice
• 4 tablespoons (60 g) unsalted butter
• 9 ounces (270 g) sorrel leaves (about 2 bunches, stemmed), cut across into narrow strips (about 6 cups)
• 1 tablespoon kosher salt