Finely mince the mushrooms along with stem or use the food processor for the task.
Heat the oil in a large pot or Dutch oven over medium heat. Add the garlic, onion, star anise, and celery. Sauté for 3-4 minutes until garlic starts turning brown.
Add the minced mushrooms to the pot. Sauté for 4 – 5 minutes, stirring occasionally, until they have released their liquid. This concentrates their flavour.
Stir in the chickpea flour (besan) and cook for 1 minute. This acts as a gluten-free binder, helping to thicken the soup later.
Pour in the vegetable stock and water. Stir in the salt and pepper. Bring the soup to a boil, then reduce the heat, cover, and let it simmer for 10 minutes.
Stir in the chopped spinach. Simmer for just 1-2 minutes, or until the spinach has completely wilted. Overcooking the spinach will dull its vibrant green colour.
Carefully transfer the hot soup mixture to a high-speed blender, or use an immersion blender directly in the pot. Blend until the soup is perfectly smooth and creamy.
Garnish with a drizzle of good olive oil, a sprinkle of fresh herbs (chives or parsley), or a few toasted nuts/seeds. Serve Mushroom Spinach Soup warm.