Preheat oven – Set oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Prepare potatoes – Peel and slice sweet potatoes into ½-inch rounds or wedges. Place in the dish.
Make the glaze – In a saucepan, melt butter over medium heat. Stir in brown sugar, white sugar, cinnamon, nutmeg, vanilla, and water/orange juice until smooth.
Coat yams – Pour glaze evenly over sweet potatoes. Toss to coat well.
Bake – Cover with foil and bake 30 minutes. Remove foil, stir gently, and bake another 20–25 minutes until tender and caramelized.
Serve – Spoon glaze over potatoes before serving. Serve warm as a holiday side dish.