It's just a tad more than that,
Katy. I usually use a fluffy potato like a
Russet because it will practically melt into the water - but don't cook it long enough for the slices to fall apart. Any old (and I do mean old - wrinkly ones work good, too) potato will work. Anyway, a recipe in bullet points:
-peel and slice enough potatoes for as many people as you are feeding, plus one more
-when very tender, drain off AND SAVE the cooking water
-mash potatoes until lumps are gone
-slowly add back water to the mash until it is very loose
--you can substitute some milk for the water if you want to make it richer or bump up the nutrition
-melt some butter in a pan, then add enough flour to make a golden brown roux for thickening
--do not skip this step. You might think it would just be easier to add less liquid to the mashed potatoes. It would work OK, but the flavor with the roux does make the soup a little richer tasting.
- add roux to simmering potato water and cook until thickened a bit. You don't want runny, but you don't want fork-able mashed
While the spuds are cooking, cut up cheese such as cheddar. The more flavorful, the better - especially if it has a bit of a bite. Pile those in the bottom of a bowl and pour the soup over when it's ready.
Sprinkle a little bit (one or two tablespoons) of finely minced onion. I've used yellow cooking, shallots, and sweet onions and prefer the sweet the best. I do not like raw onion, but this soup really needs them and it actually works for me.
You can splash a bit of vinegar on top of it all. I prefer cider or malt, but I have tried it with white, balsamic, and white balsamic. Apple is my favorite.
I suppose you can dress the soup up with other toppings. Bacon or tiny ham chunks come to mind. But I've never done that. It's a simple soup, but it is just so danged satisfying. In fact, I think I might make it sometime this weekend!
And...in the time it took you to read this, there's a pretty good chance you could have made the soup!