Preheat the oven to 400 degrees F. Grease a 9x13 baking dish with butter or nonstick spray.
Peel and slice the sweet potatoes into 1/2-inch thick slices and place them in a large bowl. Season with salt and toss to coat.
Melt the butter in a medium saucepan set over medium heat. Whisk in the maple syrup, brown sugar, cinnamon, ginger and nutmeg and bring the mixture to a low boil. Reduce the heat to medium-low and boil for 2 to 3 minutes, without stirring, until the sugar is melted and the sauce has thickened. Remove the saucepan from the heat and stir in the bourbon.
Allow the sauce to cool slightly, then pour it over the sliced potatoes; toss to coat. Transfer the potatoes to the prepared baking dish.
Bake for 20 minutes. Stir, then cover the dish with aluminum foil. Continue baking for another 35 to 40 minutes, stirring every 20 minutes, until the potatoes are soft.
Cool uncovered for at least 10 minutes before serving to allow the sauce to thicken.