Method

1. Heat the butter and olive oil together in a saucepan and add the onion. Cook gently until soft but not coloured.

2. Add the sweet potato to the pan and sauté for two minutes.

3. Add the white wine to the pan and simmer until the liquid has reduced to half its original volume.

4. Add the vegetable stock to the pan and simmer until the sweet potato is tender. Season with salt and freshly ground black pepper.

5. Turn down the heat slightly and add the double cream to the pan. Stir well, then remove from the heat and allow to cool.

6. Pour the contents of the pan into a food processor and blend until smooth.

7. To serve, reheat the soup if necessary, then pour into a cappuccino-style cup and sprinkle over the cinnamon.