To make roasted sweet potato purée, wash and scrub sweet potatoes under cold running tap water to remove any dirt. Preheat oven to 400°F (200°C), and place sweet potatoes in an ovenproof dish. (Most baking pans can’t withstand temperatures beyond 400°F [200°C], so I recommend using a cast-iron baking dish.) Bake until a skewer or knife passes through center of potato easily and flesh is soft and tender, 45 minutes to 1 hour. Let cool to room temperature. Remove and discard skins. Purée until smooth using a handheld blender, food processor, or blender.