Cook the Sweet Potatoes

• Preheat the oven to375°F (190°C).
• Place the peeled and cubed sweet potatoes in a large pot and cover with water.
• Bring to a boil and cook for 15–20 minutes, or until the potatoes are fork-tender.
• Drain thoroughly and let them sit for a few minutes to release excess moisture.

Prepare the Sweet Potato Filling

• Transfer the cooked sweet potatoes to a large mixing bowl.
• Mash until smooth, or leave a few small chunks for a more rustic texture.
• Add the melted butter, brown sugar, milk, eggs, vanilla extract, cinnamon, nutmeg, and salt.
• Beat or stir until creamy and well combined.

Prepare the Pecan Topping

• In a small bowl, combine the chopped pecans, flour, brown sugar, melted butter, and cinnamon.
• Mix with a fork until the mixture forms small, crumbly pieces.

Assemble the Casserole

• Grease a 9 × 13-inch baking dish with butter or nonstick cooking spray.
• Spread the sweet potato mixture evenly into the dish.
• Sprinkle the pecan topping over the surface if using.

Bake the Casserole

• Bake uncovered for25–30 minutes, until the filling is heated through and the pecan topping is lightly golden.
• Remove the casserole from the oven and scatter the mini marshmallows evenly over the top.

Add the Marshmallows

• Return the casserole to the oven and bake for another5–8 minutes, until the marshmallows are puffed and lightly golden.
• Watch carefully because marshmallows can brown quickly.
• For a deeper golden finish, briefly use the broiler, keeping the dish under close supervision.

Rest and Serve

• Remove the casserole from the oven and let it rest for 5–10 minutes.
• Serve warm while the sweet potato filling is creamy and the marshmallow topping is soft and toasted.