Scrub the sweet potatoes under running water before peeling. Peel and trim, then weigh 900 g of prepared sweet potato. Cut into similarly sized 2-inch (5 cm) pieces so they cook evenly.

Combine the 720 mL water, piloncillo, canela, orange peel and salt in the saucepan. Bring to a gentle simmer over medium heat, stirring for about 8–10 minutes, until the piloncillo has dissolved. Allow longer for harder pieces rather than leaving lumps in the syrup.

Carefully add the sweet potatoes, arranging them in a snug layer or two. The liquid should come partway up the pieces. Cover and simmer gently over low to medium-low heat for about 30–40 minutes, checking from 25 minutes. Turn the pieces carefully once if needed; avoid vigorous stirring. They are ready when a thin knife enters the center with little resistance. If the liquid becomes sticky before the centers are tender, lower the heat and add a little of the optional extra water, up to 60 mL total.

Use the broad slotted spoon to lift the tender pieces onto the platter. Remove and discard the canela and orange peel. Simmer the uncovered liquid over medium heat for about 8–12 minutes, only until it lightly coats a spoon. Check a small amount on a cool spoon; it will thicken further as it cools. Stop before it becomes a sticky candy-like caramel.

Take the pan off the heat. Return the sweet potatoes carefully and spoon syrup over them without breaking the pieces. Stand for 10 minutes, then divide among 6 dessert bowls and spoon over syrup. Let the syrup cool to a comfortable serving temperature before tasting.

Refrigerate in shallow covered containers within 2 hours, or within 1 hour above 90°F. Keep at 40°F or below and use within 3–4 days. Reheat leftovers to 165°F, handling the pieces gently.