If using fresh sweet potatoes, wash, peel and cut into ¼-inch thick pieces. Boil the sweet potatoes in large pot on medium heat until fork tender.
Spread the yams out evenly in a medium baking dish. Sprinkle the yams with a little nutmeg and cinnamon.
In a medium glass bowl, mix together the white sugar, pure vanilla extract, orange juice and brown sugar until well combined. Evenly coat the yams with your brown sugar mixture, adding a pinch of salt.
If using walnuts, add walnuts into the baking dish and place the pieces of butter about the dish, ensuring no corner is left empty. Bake in the oven for 10 minutes.
Remove the baking dish and stir to combine the yams in the candied mixture and buttery syrup. Bake for an additional 10 minutes.
If using marshmallows, toss room temperature mini marshmallows on top of the casserole and bake for another 5 minutes, removing when the marshmallows have begun to toast.
Note: These candied yams are sweet! If you're watching your sugar intake, you can use less sugar for this recipe. These candied yams are sweet, just like they're known for in the southern United States.