Preheat an oven to 325° F. Coat an oven-proof, 2-quart baking dish with butter; set aside.
Place the sweet potatoes into a large pot and cover with salted water. Bring to a boil over high heat, then reduce heat to medium-low, cover, and simmer until tender, about 20 minutes. Drain and set aside until cool enough to handle.
Meanwhile, place the bacon in a cast iron or other heavy-bottomed skillet and cook over medium-high heat, turning occasionally, until evenly browned and crisp, about 10 minutes. Drain the bacon slices on a paper towel-lined plate. Once cool enough to handle, chop the bacon coarsely; set aside.
Spread potatoes evenly in the prepared baking dish and top with cheese.
Bake in the preheated oven until heated through, about 20 minutes. Remove from the oven; sprinkle the potatoes and cheese with the bacon. Return to the oven and bake for an additional 5 minutes.
You may refrigerate leftovers for up to two days. Allow casserole to come back to room temperature before reheating in the oven at for 350° F for 10 minutes.
