There's a pot of soup on my stove every week to guarantee a few quick, delicious, healthy, inexpensive dinners. The easiest recipe I know is one of Julia Child's from Episode 51 of her television show, The French Chef (1963-1973). Even though I have made it many times, it is miraculous to me every time, because it only has four ingredients: potatoes, leeks, salt and water. It truly needs no other additions to be pleasurable, but my personal extra is a grinding of pepper or a pinch of India Red chili flakes. (Do not believe that yellow onions deliver the same quality of flavor.)
Julia includes a few variations of the theme to serve it cold as Vichyssoise and adding cream or watercress, which are all good ideas, if you have them on hand. Nice to know there's no need to run to the store.
Out of my own archive of material is one entitled "Making Good Soup". I still enjoy the prose, but the punch line is use home-made stock. That is what really makes good soup.
Aside from a wholesome weeknight dinner, this leek and potato version is my go to recipe for a gift for a friend that's ailing or a group that requires a plain tasting result that suits children or anyone not fond of spice. Toast Julia every time you enjoy it.