Potage Parmentier is the foundational cream soup of the French repertoire — a simple, elegant purée of leeks and potatoes named for Antoine-Augustin Parmentier, the pharmacist who championed the potato in 18th-century France. This soup teaches the template that governs all classical French puréed potages: sweat aromatics, add the principal vegetable, cover with liquid, simmer until tender, purée, finish with cream and butter. Begin by slicing 400g of leeks (white and pale green parts only) into fine rounds. Sweat them gently in 50g of butter over medium-low heat for 8-10 minutes until completely soft and translucent — they must not colour, as even slight browning changes the soup's character from pure white elegance to something more rustic. Add 500g of floury potatoes (Maris Piper, King Edward, or Bintje) peeled and cut into even 2cm dice, then 1.2 litres of chicken stock or water. Bring to a gentle boil, skim any foam, and simmer for 20-25 minutes until the potatoes collapse easily when pressed. Purée — traditionally through a moulin-légumes (food mill) on the fine disc, which produces the ideal silky-yet-textured consistency. A blender produces a smoother but sometimes gluey result from over-working the potato starch; if using one, blend briefly in short pulses. Pass through a fine sieve if absolute smoothness is desired. Return to clean heat, adjust consistency with additional stock (the soup should coat the back of a spoon but flow freely), and finish with 100ml of double cream and 30g of cold butter swirled in off the heat. Season precisely with salt and white pepper. The garnish is simplicity itself: a thin drizzle of cream, a few chive batons, and perhaps croutons fried in butter. Served cold with additional cream, this becomes vichyssoise — Louis Diat's American reinvention at the Ritz-Carlton, which has since been falsely attributed to classical French tradition.
Leeks sweated without colour for pure white result. Floury potatoes for body and natural thickening. Moulin-légumes (food mill) preferred over blender to avoid gluey texture. Finish with cream and cold butter off the heat. Served cold = vichyssoise (Diat's 20th-century invention, not classical).
A potato ricer is an excellent alternative to a food mill — it breaks down potatoes without overworking starch. Reserve the dark green leek tops for stock. For extra silkiness, mount with cold butter using a stick blender just before serving. This soup is the template for crème de champignons, crème de céleri, crème d'asperges — substitute the main vegetable, keep the method. If making vichyssoise, increase cream to 200ml and chill thoroughly; adjust seasoning when cold, as chilling mutes flavour.
Browning the leeks, producing a grey-tinged soup instead of pristine white. Over-blending, which over-works potato starch into a gluey consistency. Using waxy potatoes, which don't break down to thicken the soup naturally. Under-seasoning — potato soups absorb salt generously. Adding cream while boiling, which can cause splitting.
Le Guide Culinaire — Auguste Escoffier