Preheat the oven to 375°F (190°C): Wash, peel, and slice your sweet potatoes into thick, even rounds. Try to keep them similar in size so they cook evenly.
Make the glaze: In a saucepan over medium heat, melt the butter. Once melted, add both sugars, orange juice, vanilla extract, and all the spices — cinnamon, nutmeg, cloves, and allspice. Stir everything together until the sugar dissolves and the mixture turns smooth and syrupy.
Assemble: Arrange the sweet potato slices in a baking dish. Pour the warm glaze over the top, making sure every piece is well coated. You can gently toss them with a spoon to help distribute the syrup evenly.
Bake covered: Cover the dish tightly with foil and bake for 40 minutes. This helps the potatoes soften while soaking up all that sweet, buttery flavor.
Finish uncovered: Remove the foil, spoon some of the syrup over the top, and continue baking uncovered for another 25–30 minutes, or until the potatoes are tender and the glaze has thickened into a caramel-like sauce.
Serve and enjoy: Let the yams cool for about 10 minutes before serving — the glaze will thicken as it cools. Each bite is soft, buttery, and full of warm spice.