Heat the oil in a big soup pot over medium high-heat, add the onion and sauté until soft, about 3-5 minutes. Add chopped garlic and continue to sauté 20-30 seconds.
Add the celery, potatoes, broth, water, bay leaf, salt, pepper, and cayenne (if using). The liquid should just cover the veggies. Cover, bring to a rolling boil, turn heat down and simmer gently until potatoes are tender, about 15 minutes.
Remove from the heat, discard bay leaf and add coconut milk and fresh parsley. Let soup cool for 5-10 minutes. Using an immersion blender or regular blender, working in batches, if necessary, blend soup until smooth and silky. Squeeze fresh lemon juice, garnish with celery leaves and a thinly sliced radish. Enjoy!
