Put the cut up potatoes in a saucepan and cover with water. Bring to a boil. Cover, reduce heat to medium-low and boil for about 15 to 18 minutes, until potatoes are tender.
Drain the potatoes and mash with the butter, milk, pepper, and salt, to taste. Add more milk, as needed desired consistency.
Generously butter a slow cooker. Put the mashed potatoes into the slow cooker; cover and keep on LOW for up to 2 hours.
Or, refrigerate the prepared potatoes for 1 to 2 days. Let them stand at room temperature for 1/2 hour. Put the potatoes in a generously buttered slow cooker; cover and cook on LOW for about 3 hours, stirring a few times.
Calories per serving: 309