Preheat your oven to 350°F (175°C) and allow it to preheat fully for about 10 minutes.

Peel 4 pounds yams and slice them into 1/4-inch-thick rounds using a vegetable peeler and sharp knife.

In a small bowl, whisk together 1 teaspoon ground cinnamon, 1/2 teaspoon ground nutmeg, 1/4 teaspoon ground ginger, and 1/4 teaspoon salt until evenly combined.

In a large mixing bowl, whisk together 6 tablespoons melted butter, 1/2 cup packed brown sugar, and 1/4 cup granulated sugar until smooth.

Add the spice mixture and 2 tablespoons orange juice or vanilla extract to the butter-sugar mixture, stirring well to combine.

Arrange half of the yam slices in a single overlapping layer in the 9 by 13-inch baking dish and pour half of the butter-sugar sauce over them, then layer the remaining yams and pour the rest of the sauce on top.

Cover the baking dish tightly with foil and bake at 350°F for 35 to 40 minutes, or until the yams are fork-tender.

Remove the foil and scatter 3 cups mini marshmallows or halved regular marshmallows evenly over the yams. Bake uncovered at 350°F for 8 to 10 minutes, or until the marshmallows are puffed and golden brown.

Let the dish rest for 3 to 5 minutes before serving to allow the sauce to set and the marshmallows to firm up.