Peel the potatoes, cut large tubers into pieces. Try not to cut the potatoes too finely. This will cause them to lose more starch.
Place the potatoes in boiling, salted water. Leave to cook until tender, about 40-50 minutes.
Heat the milk over medium heat. Reduce heat to low and add butter. Melt the butter, stirring constantly.
After the potatoes are ready, drain the water and mash them with a masher. Choose a simple wooden or perforated stainless steel masher. With it, the puree will be more airy. You can also use a food processor, blender or mixer to prepare the puree, but with them it will be more viscous and sticky.
Pour warm milk and butter into the potatoes. Mash everything again well so that there are no lumps, and add salt to taste.
Before serving, cover the pot with the puree with a towel and leave it for a while so that the side dish acquires the desired consistency.