The most memorable mashed potatoes manage to be both fluffy and buttery at once. Too much butter and they’re heavy; not enough and they’ll seem wimpy. Here’s where choosing the right spud for the job really matters. The texture of a potato after cooking depends on its structure and moisture content. Some varieties, such as Idaho bakers, have low moisture and cook up to be light and airy. Beaten with butter and cream, they make a fluffy mash. High-moisture potatoes, such as red potatoes or new potatoes, can turn “gluey” when beaten. But because they have such a distinctly earthy, nutty flavor, I like to add just one or two to the pot.