Preheat your oven to 400°F (200°C). In a medium saucepan, combine the dark brown sugar, fresh orange juice, butter, cinnamon stick, bourbon (if using), grated nutmeg, and a pinch of kosher salt. Bring to a gentle boil, then reduce heat and simmer for about 10 minutes. Remove and discard the cinnamon stick.

Peel the medium yams, then slice into 1/2-inch thick rounds. Arrange the slices in a single layer for layering.

Grease a 13" x 9" baking dish with additional butter. Layer the sliced yams in the dish, slightly overlapping. Pour the syrup evenly over the yams.

Cover tightly with aluminum foil and bake for 30 minutes. Remove foil and baste yams in syrup every 15 minutes. Continue baking uncovered for 50 to 60 minutes, until tender and glazed.

Remove from oven and allow to cool slightly before serving.