Robuchon's pomme purée — the most discussed and most copied potato preparation in modern restaurant cooking — uses a butter-to-potato ratio that famously shocked diners and critics when it was revealed: equal weights of butter and cooked potato. The technique produces not a simple mashed potato but a preparation of extraordinary silkiness, richness, and depth. The precision requirements: the specific potato variety (Ratte or BF15 — waxy, low-starch, fine-grained), the cooking method (gentle steaming or boiling in skin), the drying after cooking, and the working of the butter through a fine drum sieve (tamis).
- **The potato variety:** Ratte (small, fingerling-type, waxy, low moisture) or BF15 — a high-moisture floury potato like Russet produces a gluey purée that cannot absorb the butter quantity. [VERIFY] Robuchon's potato specification. - **Cooking in skin:** The potato is cooked with its skin on — the skin prevents excessive water uptake during cooking. Peeled before puréeing while still very hot. - **Drying:** After cooking, the potato is returned to the dry pot over medium heat and stirred until all steam has evaporated — any residual moisture prevents butter absorption and produces a broken purée. - **The tamis (drum sieve):** The cooked potato is pushed through the fine mesh of a drum sieve — this removes every fibrous element and produces a purée smoother than any food processor can achieve. - **The butter:** Cold butter, cut in small pieces, beaten into the hot dry potato purée one piece at a time — each piece fully incorporated before the next is added. The potato must be hot enough to melt the butter while the cold butter moderates the overall temperature. - **The hot milk:** Added at the end to achieve the correct flowing consistency — the milk brings the purée to the desired pourable, silky texture without breaking the butter emulsification. Decisive moment: The butter incorporation temperature. The potato must remain hot enough to melt each butter piece, but not so hot that it breaks the emulsion. If the purée becomes greasy (the emulsion has broken — the butter fat has separated from the potato's starch-water), the temperature was too high.
The Complete Robuchon