Fill a large saucepan one-third full with cold water. Cut the potatoes into quarters and add them to the saucepan. Cover the potatoes with 1 more inch of water and add 1 tablespoon of salt. Cover the saucepan and bring to a boil, then uncover, reduce the heat and simmer the potatoes until easily pierced with a knife, about 15 minutes; drain.
In the same saucepan, heat the milk, butter and a pinch of salt and pepper until the milk is steaming. Remove from the heat. Add the potatoes and mash. Season the mashed potatoes to taste with salt and pepper. Serve with your choice of mix-ins.