Creating Sweet Potato Casserole with Marshmallows is simple if you follow these easy steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C).
2. Prepare Sweet Potatoes: Peel and cut the sweet potatoes into chunks. Boil them in a large pot of salted water until tender, about 15-20 minutes.
3. Mash Sweet Potatoes: Drain the sweet potatoes and return them to the pot. Mash until smooth.
4. Mix Ingredients: In a large bowl, combine the mashed sweet potatoes, granulated sugar, melted butter, milk, eggs, vanilla extract, cinnamon, nutmeg, and salt. Mix until well combined.
5. Transfer to Baking Dish: Pour the sweet potato mixture into a greased 9×13-inch baking dish, smoothing the top with a spatula.
6. Add Topping: Evenly distribute the mini marshmallows over the top of the sweet potato mixture. Sprinkle chopped pecans or walnuts if desired.
7. Bake: Place in the preheated oven and bake for 30-35 minutes, or until the marshmallows are golden brown and the casserole is heated through.
8. Cool Slightly: Remove from the oven and allow to cool for 10-15 minutes before serving.

These steps will guide you in creating this incredible casserole effortlessly.