Top and tail the beetroot, then peel it under cold running water. Cut each one into eight roughly equal pieces. Cut the celery into thick slices. Peel the onion and cut it into eight pieces. Peel the garlic and chop it roughly. Put all these ingredients into a large saucepan, add the olive oil and stir to coat the vegetables. Cook the vegetables over a medium heat for 10 minutes, stirring occasionally. Add the cumin, chilli flakes and a generous twist of black pepper and continue to cook for a further 10 minutes.
Pour the vinegar and vodka (optional) into the pan, stir the vegetables well and continue to cook until the moisture in the pan has evaporated away. Add the stock and bring the mixture to the boil. Then lower the heat, put a lid on the pan and simmer for an hour, checking and stirring regularly. Use the point of a sharp knife to check that the beetroot is tender, then take the pan off the heat and allow the soup to cool.
Transfer the soup to a blender or food processor and blend until very smooth. Return it to the saucepan, pour in the coconut milk and reheat, stirring continuously. Check the seasoning and consistency – if you would like a thinner soup, add a little more water.

Makes 1 litre / 4 servings

Tip: Reserve a little coconut milk to add a swirl to each bowl before serving, or decorate with a few drops of chilli-flavoured oil.