I make abysmal mash. It is always too lumpy or too smooth or too watery or too dry. I can do it from jacket potatoes but that always seems a waste of good jackets. However: the slow cooker!
I first saw slow cooker mash on mumsnet, but it seems to have disappeared. Googling comes up with a load of wacky American recipes involving chicken broth and onion powder. So, just get a load of potatoes. Peel them slice them chop them dice them (I went for chunks about 1.5″ across). In the slow cooker with a minute dribble of water, some salt and a large lump of butter. I put it on high because I didn’t get them peeled until midday – they were done by 5.30. Mash them, add milk, mash some more. Scoff.