Grease a 9 by 13-inch pan with butter. Wash but do not peel the sweet potatoes.
Plunk the potatoes in a large pot of boiling water and cook them until fork tender (but not total mush)—about 45 minutes.
Let the potatoes cool until you can touch them. In the meantime, preheat the oven to 350° F and, in a small bowl, combine the cinnamon and brown sugar. Peel and slice one of the oranges, then cut the fruit in quarters (or do what I really do and rip the orange slices into bite-size pieces).
Once you can pick up the potatoes, peel and cut into 1/2-inch slices.
Create one layer of potatoes in your prepared pan. Top with butter cubes, a sprinkling of the sugar mixture, and a few pieces of orange. You want the potatoes evenly covered with butter, orange pieces, and sugar—but no need to get precise with it. It's only sweet potatoes.
Continue layering potatoes, butter, sugar, and orange pieces until you've just about reached the top of the pan or you've run out of sweet potatoes. On the last layer, instead of orange pieces, squeeze the two remaining oranges over the top. Add some more butter, too. Because.