Place the potatoes, water, vegan buttery spread, non-dairy milk, and salt in a 6 quart slow cooker.
Place the lid on and cook for 4 hours on high heat.
You may want to check the potatoes after the third hour - if they look like they are drying out, you can add a little more warm non-dairy milk.
Once the potatoes are tender, use a potato masher to mash them in the slow cooker. Season with more salt and pepper if desired.
Notes
The butter and milk will slightly caramelize around the edges of the slow cooker. This is normal, and will result in a nice flavor. However, you can scrape it off with a spoon if you want.If you aren't dairy free, go ahead and use regular milk and butter.I haven't tried cooking these on low for 8 hours - doing so may result in discoloration or gummy potatoes.Store leftover mashed potatoes in an airtight container in the refrigerator. They should stay fresh for about 3-4 days.