Cook onion and garlic in butter over medium high heat until onion is translucent, about 5 minutes. Add chicken stock, water, carrots, leeks, green onions, habanero peppers, spinach, and watercress. Bring to a low boil, and cook for 30 minutes, or until carrots are soft. Remove from heat, and allow to cool for 30 minutes.
Puree in a blender or food processor until smooth. Return to the pot, and simmer on low heat for 15 minutes before serving. Serve with a drizzle of olive oil or vinegar, or both, if desired.