Preheat the oven to 375°F. Lightly butter a 9x13-inch baking dish.

Wash, peel, and slice the sweet potatoes into approximately ½-inch-thick rounds.

Arrange the sweet potatoes in the prepared baking dish.

In a medium saucepan over medium heat, combine the butter, brown sugar, cinnamon, and nutmeg.

Cook, stirring frequently, until the butter is melted and the brown sugar has dissolved.

Remove the saucepan from the heat and stir in the vanilla extract.

Pour the butter and brown sugar mixture evenly over the sweet potatoes. Gently toss or stir until the slices are well coated.

Cover the baking dish tightly with foil and bake for 30 minutes.

Remove the foil and carefully spoon some of the syrup from the bottom of the dish over the sweet potatoes.

Return to the oven and bake uncovered for another 20–25 minutes, or until the sweet potatoes are fork-tender and the sauce has thickened into a syrup.

Let cool for about 10 minutes before serving.