Preheat oven to 375°F (190°C). Peel (optional) and core the apples, then slice them into even wedges or chunks. Place them in a mixing bowl.
In a small bowl, mix the melted butter, brown sugar, cinnamon, nutmeg, salt, and vanilla extract. Pour this mixture over the apples and toss until evenly coated.
Transfer the coated apples into a baking dish. Add the water or apple juice to the bottom of the dish. Cover with foil and bake for 20 minutes. Remove the foil and continue baking for another 15–20 minutes, or until apples are fork-tender and caramelized.
Serve straight from the oven, on their own or topped with whipped cream, yogurt, or vanilla ice cream.