Here is how I do them.
First I bake all the sweet potatoes. You can do this the day before. Then I peel them. This is the most labor intensive part. I'm sure you could always peel them beforehand and then boil, or however you like to cook them.
Then slice them widthwise into little circles, about a 1/2" thick. Butter a casserole dish. Put a layer of sweet potatoes down. Dot with butter and sprinkle with brown sugar. Put another layer of potatoes, dot with butter and sprinkle with brown sugar. Do the same again, but this time add some little marshmallows on top (some people don't like this, but my family does).
Cover with aluminum foil, and bake either beforehand or at the persons house, until everything is melted and bubbly. Take the aluminum foil off for the last 10 minutes or so so the top gets all nice and browned.
You can make this the day before and just keep refrigerated.
You can also add: nutmeg, cinnamon, orange juice, or anything else that sounds good.
Some people whip baked sweet potatoes, but I've never done that myself.