Mashed potatoes are something that I really don't over think, I just make 'em. Which is rare for me, being a baker, I am all about precision, but when it comes to mashed potatoes I wing it.
My preferred method, red skin or yukon gold (so I don't have to peel them), cubed fairly small, boiled in salted water (good amount of salt). Drain them, put a good hunk of butter in the bottom of the pan (more than you think is healthy), return the potatoes to the pan, run the hand mixer through them adding salt and pepper as you go to taste. If they are too thick, thin them down with milk or a bit of cream. I usually go a little heavy on the liquid, because as they sit a bit they will thicken.