Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish and set aside.

Place the sweet potato chunks in a large pot and cover with cold water. Bring to a boil and cook until fork-tender, about 15 minutes. Drain well.

In a mixing bowl, mash the hot sweet potatoes with butter until smooth. Stir in brown sugar, cinnamon, salt, nutmeg (if using), vanilla extract, and beaten eggs until creamy and well combined.

Transfer the sweet potato mixture to the prepared baking dish, smoothing the top with a spatula.

Sprinkle mini marshmallows evenly over the surface. If desired, add chopped pecans for extra texture.

Bake for 20–25 minutes, or until marshmallows are golden brown and the casserole is heated through.

Remove from the oven and let rest for 5 minutes before serving.