Heat oil in a big pot over medium high heat, and add the onion, stirring occasionally, letting the onions get golden, about 5 minutes.
While the onions are cooking, roughly chop the garlic, celery and potatoes
When the onions are golden add the garlic and stir 1-2 minutes, until fragrant. Add the celery, potatoes, broth, water, bay leaf, salt, pepper, and cayenne. The liquid should just cover the veggies. Cover, bring to a rolling boil, turn heat down and simmer gently until potatoes are tender, about 10 minutes.
Turn heat off, remove bay leaf and add the fresh herbs and just wilt them (don't cook herbs or you lose the vibrant colour).
Using an immersion blender, blend until very silky smooth - OR if using a regular blender, let cool before blending in smaller batches. (Don't fill blender more than half and cover lid tightly with a towel, starting on lowest seting to avoid blender 'explosion'.)
Blend well, a full minute, until herbs are fully blended, creating a vibrant coloured soup. For extra 'green' colour, add a handful of raw spinach or more fresh parsley. Place it back in same pot over low heat. Stir in your choice of cream.
Crispy fry celery leaves and toast pumpkin seeds to garnish