roasted apple, onion and sweet potato soup

Despite their name, sweet potatoes are not related to potatoes. However, they will do most things that potatoes do. You can roast, bake or mash them, and they are a great thickener for soups. They have their own natural sweetness, which is why I have added a few tart apples to help balance the flavors. They seem to enjoy being mixed with flavors such as ginger, chili, lime and coriander, as well as the fennel and cumin used here.

• Preheat the oven to 450°F. Dry-fry the fennel and cumin seeds in a heavy frying pan over moderate heat, turning or stirring frequently, for 3 minutes or until they start to go brown and pop. Coarsely crush the seeds using a pestle and mortar.
• Put the onions and sweet potatoes into a roasting dish. Core and roughly chop 2 apples, and add them to the dish.
• Sprinkle the crushed seeds over the vegetables and apples, and season. Drizzle 2 tablespoons olive oil over the top. Roast for 25 minutes, then turn the vegetables over and roast for an additional 25 minutes. The onions should be tender when pierced with a knife. Remove 2 potato chunks and 8 onion quarters, and set them aside.
• Put half the remaining vegetables into a food processor with half the stock, and process to a smooth puree. Transfer to a saucepan. Repeat with the remaining vegetables and stock. Warm the soup through over a gentle heat.
• Core and roughly chop the reserved apple. Roughly chop the 2 reserved potato chunks and the 8 reserved onion quarters. Heat the remaining oil in a frying pan, add the chopped apple and sauté for 5 minutes, or until golden.
• Add the chopped potatoes and onions and warm through, stirring every now and then, over low heat. Season with salt and pepper to taste.
• When the soup is warm, divide it among four warm bowls, and spoon a little of the chopped onion, potato and apple mixture into the center of each bowl. Scatter the fresh tarragon leaves over the soup, and serve.