Saute onion in a large pot with oil.
Add 1 liter broth/stock. Stir
Add the salt
Add the leeks and simmer for 15 minutes
Use immersion blender* to puree the soup
Add water to increase volume or if you prefer a looser or thinner soup.
Add the optional ingredients to the pot while on low heat. Stir to combine well!
Ready to serve!
* several choices here: use a hand-held immersion blender or a regular blender OR don't blend at all. Or blend a little but leave some leeks in the pot. Your Choice!