In a large pot or Dutch oven, combine the sweet potatoes, butter, brown sugar, granulated sugar, cinnamon, nutmeg, salt, vanilla extract, and water.
Bring the mixture to a boil over medium-high heat, then reduce the heat to low, cover, and simmer for 25-30 minutes, or until the sweet potatoes are tender but still hold their shape. Stir occasionally to prevent sticking.
If desired, transfer the sweet potatoes to a baking dish and bake in a preheated oven at 350°F (175°C) for 20-30 minutes to intensify the caramelized flavor.
Serve hot and garnish with pecans or a sprig of rosemary, if desired.
