Preheat oven to 375 degrees.
In a bowl, stir to combine the white sugar, brown sugar, nutmeg and cinnamon
Peel yams and slice them approx. ¼ inch thick
In a baking dish, place a layer of the cut yams.
Generously sprinkle the sugar mixture onto the yams.
Place another layer of yams on top of the sugar mixture, and repeat until the dish is full.
Combine the water and vanilla in a cup and gently pour it around the edge of the dish.
Place the butter cubes around the top of the dish.
Top with any remaining sugar mixture.
Cover tightly with foil and bake for 45 – 60 minutes.
When the potatoes can be pierced (with a fork, toothpick, etc.) without falling apart they are done!
Let rest before serving. Enjoy!!