
Preheat the oven to 400º. Whisk together the brown sugar, butter, maple syrup, 1 tablespoon of water, salt, cinnamon, ginger, and nutmeg in a large bowl, plus bourbon, if using. Add the sweet potatoes to the the sugar mixture and toss to coat. Pour into 13-by-9-inch casserole dish. Spread the sweet potatoes into an even layer and pour any leftover sugar mixture over them.
Bake the sweet potatoes until tender and the sauce thickens into a glaze, 45 to 60 minutes, stirring every 15 minutes. Let cool for 10 minutes before serving.