Place potatoes in a large saucepan and cover with water. Bring to a boil, add salt, then reduce heat to medium and cook until tender, about 15 to 20 minutes. Drain potatoes in a colander and discard cooking water. Return potatoes to the pot, set over medium heat. Stir potatoes constantly for 2 to 3 minutes to remove any excess liquid.
Add butter; using a handheld potato masher, mash butter into potatoes. Gradually add milk; stir to mix. Season with salt and pepper to taste. Serve hot.