Peel and wash the potatoes (unless using new potatoes in which case skins can optionally be left on). Cut into roughly equally-sized chunks/cubes (to speed cooking). Rinse the potatoes several times.
Salt some water liberally, add the potatoes and heat to a boil.
Boil until tender (I test with a fork on a bigger chunk).
Drain thoroughly, transfer to a large mixing bowl, and allow to sit and steam uncovered by themselves for several minutes for the excess water to evaporate.
Add just the butter (I'd estimate roughly 2-3 tablespoons for 3-4 potatoes, but again just to taste) and the salt.
Roughly mash the potatoes together with just the butter and salt with a potato ricer or an electric mixer.
Add a few heaping spoonfuls of sour cream (and probably some more salt) and mix/rice together.
Slowly add milk (warmed up in the microwave) while mixing until desired consistency is reached. Taste and add extra salt if necessary.