There’s a lot of rubbish written about mashed potato. Basically make sure that the potatoes are soft enough to mash without lumps. Add milk / butter, salt / pepper, as desired.
The mashed potato in France never tastes like ours, they call it Puree de Pommes de Terre and are very specific about how it’s made, using a potato ricer and much too much butter than is healthy. Recipes for this super rich version are aplenty online.
