Prepare the Sweet Potatoes:

1. Cook the Sweet Potatoes: Peel and cube the sweet potatoes into 1-inch pieces. Place them in a large pot and cover with water. Bring to a boil and cook for 15-20 minutes or until the sweet potatoes are tender when pierced with a fork.
2. Drain and Mash: Drain the sweet potatoes and return them to the pot. Mash with a potato masher or use an electric mixer for a smoother texture.

Prepare the Sweet Potato Mixture:

3. Mix the Ingredients: Add the softened butter, brown sugar, vanilla extract, cinnamon, nutmeg, salt, eggs, and milk to the mashed sweet potatoes. Stir until well combined and smooth.
4. Taste and Adjust: Taste the mixture and adjust the seasoning if necessary. If you like a sweeter casserole, you can add a bit more brown sugar.

Prepare the Topping:

5. Make the Topping: In a small bowl, mix together the chopped pecans and brown sugar. If you prefer a marshmallow topping, skip this step and set aside the mini marshmallows for later.

Assemble the Casserole:

6. Transfer to Baking Dish: Pour the sweet potato mixture into a greased 9×13-inch baking dish, spreading it out into an even layer.
7. Add the Topping: Sprinkle the pecan-brown sugar mixture evenly over the top of the sweet potatoes. If using marshmallows, add them on top after baking for a toasted finish.

Bake the Casserole:

8. Bake the Casserole: Preheat your oven to 350°F (175°C). Bake the casserole for 25-30 minutes, or until the topping is golden brown and the casserole is heated through.
9. Optional – Add Marshmallows: If you’re using marshmallows, add them in the last 5-7 minutes of baking and continue baking until the marshmallows are golden and slightly puffed.