Preheat oven to 400°. Butter a medium baking dish. 

In a medium saucepan, combine sugar, orange juice, butter, cinnamon, nutmeg, bourbon if using, and salt. Stir to combine and bring to a boil over medium heat. Reduce heat to a simmer and cook until sugar mixture has thickened slightly, about 10 minutes.

Peel yams and slice into 1-inch chunks, then layer in prepared baking dish. Pour thickened glaze over yams and cover dish with aluminum foil.

Bake for 30 minutes, then remove foil and bake an additional 30, basting with sauce once or twice while cooking.

Let cool slightly before serving.