Add chopped potatoes to a greased slow cooker. Cover and cook on high for 2-3 hours or on low or 5-6 hours on low.
When potatoes are cooked and fork-tender, add all remaining ingredients (let the butter melt for a couple of minutes). Use a hand mixer or a masher to mash the potatoes. (*see note) Serve warm.
*recipe adapted from Slow Cooker Mashed Potatoes **This recipe can easily be doubled for large groups - just increase the cooking time by 1-2 hours. **Although I have never had this happen to my potatoes, I have heard some people complain of "gluey" potatoes after mashing. Click HERE for my tips on making perfect, never-gluey mashed potatoes!