1. Fry the celery, garlic, broccoli and baby marrow in a little oil until al dente. Add the vegetable stock and bring to the boil. Remove from the heat.
2. Transfer the soup to a food processor, add the cashew nuts and pulse until smooth. Add the spinach and herbs and pulse until well combined. Season with lemon juice.
3. Add the yoghurt, pulse until smooth, then season with salt and pepper.