Okay, after 30 years I have finally mastered the ultimate sweet potato/marshmallow casserole. I've tried every combination. Canned yams, fresh baked yams, sweet potatoes, both baked and boiled.....mixed in chunks before baking with the other ingredients and cooked then put in a casserole and topped, and put in the casserole and then adding the other ingredients. I've finally got it down and my kids make me make it every Christmas and Thanksgiving, and lucky you, I'm sharing. After all these years and experiments, it is, of course, ridiculously easy. Use serrated steak knife to scrape off skin of raw SWEET POTATOES (NOT yams!) just like you would carrots, and remove eyes. I just learned this at Thanksgiving. It's easier and quicker than peeling, and wastes zero of the flesh. Cut up those puppies in whatever size you like. They cook much quicker than white potatoes, I assume because there's sugar in them and maybe they get hotter quicker. I don't know, but you can cut them any size, just try to get them uniform. Boil in salted water until tender, water needs to cover them. It doesn't really take very long. Drain off water (I almost always just dump my potatoes in a strainer, then back into the pot and leave the lid off to let steam escape. Makes for a little drier, better mash). Mash them just like you would regular potatoes...with a lot of butter and real cream. Then add brown sugar. I put in about 1/2 cup, more or less. Maybe more. It depends. Put them in a casserole, top them with marshmallows and stick them in the oven at whatever temp....if you really watch them you can just broil them for a few minutes to brown the marshmallows but yikes be careful. I always forget when I use a broiler. My kids love these better than any, and like I said, they're the easiest. Me, I like baked sweet potatoes with butter, salt and pepper. Sometimes sour cream. But then I've been working on this stupid recipe for 30 years and I'm about sick of it. But I finally got it right, and consistent.