A delightful and light soup made from a base of water, olive oil, and salt, with cubed vegetables and chicken or ham (optional.)
Peel the outer skin from vegetables that need it (e.g. carrots, onion, parsnips, celery root and garlic) and wash the skin of the rest of the vegetables.
Cut the vegetables except for the leeks and garlic into very small cubes, about the size of your thumbnail.
Slice the white part of the leek off from the green part, cut off the bottom strings from the white part opposite the green stem, slice the leek in half lengthwise and wash it well, separating the inner layers to let water run through where dirt can be hiding. Cut each lengthwise piece of the leek into half thin half-moon slices.
Put all the cut vegetables and meat (if using) into a large bowl. (Cut any meat into cubes roughly the size of the vegetables, or if it is cooked chicken, maybe shred it.)
Add the clove of garlic.
Bring 4 cups of water, the olive oil, and salt to a rolling boil on the stovetop. (When you start the water/oil/salt heating, small bubbles appear around the edges. That stage is a simmer, which is how the soup should look when it cooks with all the ingredients. But at this first stage, it must be heated to a higher temperature, until large bubbles appear all over the surface of the liquid.)
Add the vegetables (and meat.) Put the lid on the pot halfway, so that air can escape from the pot. Turn the light on the stovetop down so that the soup is simmering (small bubbles, mostly on the sides) and cook for 30 minutes. Taste - add pepper and more salt if desired.
If desired, add a crouton with melted cheese and/or herbs. You can also add parsley and/or other herbs, either minced or pounded into paste with a teaspoon of olive oil.