Heat the oil in a large saucepan. Add the onion and garlic, and cook until soft but not browned. Add the white wine and allow most of it to evaporate.
Add the Jerusalem artichokes and stir. Cook for 2 minutes, then add the potato. Add the chicken stock, then add water to cover. Bring the mixture to the boil, then reduce to a simmer. Add salt and pepper, and simmer until the vegetables are tender, about 15 minutes.
Meanwhile, add the chopped chorizo to a small frying pan and heat over medium heat. Cook the chorizo, stirring occasionally, until it is crisp. Remove the bits from the pan and place on a piece of kitchen paper to cool and soak up excess oil.
Once the veg is soft, puree the soup using an immersion blender or a liquidiser. While pureeing, add the yoghurt. Add the milk in a steady stream till you reach your desired consistency.
Add the ground nutmeg, then taste to adjust the salt and pepper as desired. Serve bowls of soup with a sprinkling of chorizo bits and chopped parsley.