100ghome-made or Greek yogurt, thinned with a little milk an seasoned with 1 garlic clove crushed to a paste with sea salt and black pepper
Heat the oil in a large saucepan over a medium heat. Add the onion and a pinch of salt.
Cook for 10 minutes, stirring occasionally until the onion begins to colour. Now add the garlic and cumin and cook for 2 more minutes to release their flavour, followed by the beetroot and potato.
Pour in the water, bring to a gentle simmer and cook until soft, about 15 minutes (I don't think I chopped mine small enough as it took much longer to soften).
Place the vegetables and the cooking liquid in a blender or food processor and blend until just smooth. You may need to do this in two stages. Return to the pan, add the vinegar, half the parsley and salt, and pepper to taste, bearing in mind you may need more salt than you think to balance out the acidity of the vinegar.
Serve with a little yogurt on top, the rest of the parsley and an extra drizzle of olive oil.