Preheat your oven to 350°F (175°C).
Peel the sweet potatoes and cut them into 1-inch thick slices or cubes.
In a large saucepan, combine the brown sugar, butter, water, vanilla extract, cinnamon, nutmeg, and salt. Heat over medium heat, stirring until the butter is melted and the mixture is smooth.
Add the sweet potatoes to the saucepan and stir gently to coat them in the syrup.
Transfer the sweet potatoes and syrup mixture into a baking dish, spreading the sweet potatoes evenly.
Cover the dish with aluminum foil and place it in the preheated oven. Bake for 30 minutes.
After 30 minutes, remove the foil and stir the sweet potatoes gently. Return to the oven and bake uncovered for an additional 15 minutes, or until they are tender and caramelized.
If desired, sprinkle the chopped nuts over the top for added crunch. Serve warm.