Place the celery, garlic and onion on a large rimmed baking sheet and drizzle with olive oil and sprinkle with salt and pepper. Roast in the oven for 45 minutes.
While the vegetables roast, bring the vegetable broth to a boil and add the potatoes. Boil for 8-10 minutes, or until very tender. Add the celery mixture to the broth. Allow to cool slightly. Working in batches, puree the soup and pour into a clean stock pot. You can also pass through a fine mesh sieve if you'd like the soup to have less texture. Add the coconut milk and heat over medium heat until the soup is hot, stirring occasionally. Season again with salt and pepper to taste. Sprinkle a little chili flake before serving.
Recipe by Farmgirl Gourmet at https://www.farmgirlgourmet.com/2015/12/roasted-celery-soup-recipe.html