Tip the parsnips, carrots, onions, garlic and curry powder into a slow cooker, and mix well so all the vegetables are coated in the curry powder. Pour in the vegetable stock, then mix again and season well.

Cook on low for 8 hrs. Transfer to a blender and blitz until smooth. If you prefer your soup a little looser, you can stir in a few splashes of boiled water from the kettle. Divide between bowls and season with ground black pepper before serving. Once completely cool, the soup will keep frozen up to three months. Defrost completely in the fridge overnight, then reheat in a pan until piping hot before serving.