Clean the leek by chopping the base and the top of the upper green section. Make a lengthwise cut and wash the leek, notice if the upper green section has some dirt inside and make sure to wash it properly.
Thinly slice the leek and garlic cloves.
In a medium sized pot over medium-low heat add the olive oil. Sweat the leeks and the garlic. Cook until the leeks appear golden brown. Take out of the pan ¼ of the cooked leeks/garlic and reserve.
Then add the white beans, broth, thyme and black pepper to the pot. Allow to bubble and simmer until the leeks are completely soft, about 5-6 minutes. Stir often to avoid sticking at the bottom of the pot.
Blend with a hand blender or regular blender until you have a creamy and uniform soup.
Transfer back to the pot and place over medium heat. Add diced potato and salt, mix into the soup.
Allow to bubble and simmer until the diced potato is cooked through and the soup has reduced (8-10 minutes). By the end taste the soup and add extra salt per taste if necessary.
If you want to make croutons I suggest a bread fried with a little oil or butter and crushed garlic. It fits really nicely.
Serve the soup with reserved browned leeks/garlic, parsley leaves, low fat sour cream, croutons and feta.