Peel the pumpkin and sweet potatoes and chop them into large chunks, about 5 cm (2 inches) in size.

Peel the onion and cut it into quarter wedges.

Place the vegetables onto a large baking tray.

Drizzle the olive oil over the vegetables, and sprinkle over the ground cinnamon and freshly ground nutmeg.

Roast the vegetables for about 1 hour until they are golden and cooked through.

When the vegetables are nearly done, bring the vegetable or chicken stock to the boil.

Place the roasted vegetables into a large saucepan, and pour over just enough stock to cover the vegetables.

Bring the saucepan to a gentle simmer.

Take the saucepan off the heat.

Use a stick blender to purée the soup. Alternatively, purée the vegetables with some stock in a blender, though you will have to do this in a few batches.

If the soup is a bit thick, add some more stock or hot water to thin out the soup to your liking.

Heat the soup until it is gently simmering and taste for seasoning.