I use this recipe that came with my Robot Chef 30 years ago, for "Potage Parmentier" ::::
Slice some potatoes very thinly ( as if you were going to make crisps with them ! )
Slowly saute in butter with a thinly chopped leek, until soft, and then add some milk and a good dash of single cream, and a small handful of Rosemary. Simmer this until everything is soft.Then liquidise with your Robot Chef ( or any other liquidiser ! ) until it is really smooth and has no lumps. Add salt and black pepper to taste.
If you stir in a little more single cream into it just before serving, it will be even nicer !
The French have this cold as well as hot, although I prefer hot.
A friend of mine pinched the recipe years ago, and adds a big handful of watercress to hers !