3 red onions, halved lengthwise, then cut into thin slices
3 pounds sweet potatoes, halved lengthwise, then cut into thin slices
2 cups apple cider
1 teaspoon salt, or to taste
Freshly ground black pepper to taste
Preheat the oven to 350 degrees.
Mix all ingredients together in a baking dish. Cover with foil and bake 1 hour. Remove the foil and continue to bake 30 minutes more, or until the sweet potatoes are tender.