Peel and slice the sweet potatoes, about 1/2 inch thick.
Spray a 9x13 baking dish with nonstick spray and preheat your oven to 375 degrees Fahrenheit.
Add the potatoes to the dish and sprinkle with salt.
In a medium saucepan, combine unsalted butter, maple syrup, brown sugar, cinnamon, nutmeg, and ginger.
Heat over medium-high heat, stirring constantly, until melted and boiling softly. Simmer for 2 minutes and remove from the heat. Stir in the vanilla.
Pour this mixture over the sweet potatoes in the dish and stir.
Bake at 375 for 60 minutes total, stirring the potatoes every 20 minutes.
If desired, garnish with fresh rosemary.