Mashed potato or potatoes is one way of serving potatoes. It is made by mashing freshly-boiled (peeled or unpeeled), or sometimes baked, potatoes with a ricer, fork or potato masher. Dehydrated and frozen mashed potatoes are also available.
The use of "floury" types of potato is usually recommended, although "waxy" potatoes are sometimes used for a different texture. Butter (or vegetable oil) and milk or cream is usually added to make smooth, well-flavoured mashed potato. Basic seasonings include salt, pepper, and rosemary. Other ingredients and seasonings include: garlic, cheese, bacon bits, sour cream, crisp onion or spring onion, mustard, spices, chopped herbs such as parsley, white turnip, and wasabi. A French variation adds egg yolk for Pommes duchesse piped through a pastry tube into wavy ribbons and rosettes, brushed with butter and lightly browned. In low-calorie recipes, milk, cream, and butter are replaced with soup stock or broth.
Mashed potato can take on a glue-like consistency when the starch grains in the potato burst. To avoid this potatoes should not be overcooked. Thinly slicing the potatoes allows them to cook evenly where larger pieces would be either overcooked on the outside by the time heat had penetrated to cook the center, or raw inside. Heston Blumenthal recommends cooking the sliced potatoes for 40 minutes at a controlled temperature of 70°C. To avoid the need for temperature control the potatoes can be boiled until just cooked (10 to 12 minutes).
Potatoes are best mashed before adding butter, etc.; the butter or liquid lubricates the lumps of potato making them easier to break up. If a food processor or similar is used for mashing it will mechanically break the starch grains and produce an undesirable gluey result.