Sweet potato casserole topped with a crunchy pecan streusel or toasted marshmallows is a beloved vegetarian holiday family tradition. Sweet, creamy, and comforting, it's a Thanksgiving table essential across the South.
Preheat your oven to 350°F (175°C). Scrub and peel the sweet potatoes, then cut into large chunks for even cooking.
Place sweet potato chunks in a large pot and cover with water. Bring to a boil, reduce heat to medium, and simmer for 20–25 minutes until very tender. Drain thoroughly to prevent excess moisture.
Mash the hot sweet potatoes in a large bowl. Add 0.25 cup butter, granulated sugar, milk, eggs, vanilla extract, salt, and cinnamon. Beat until smooth and creamy; consistency should be thick but spreadable.
Transfer the sweet potato mixture to a greased 9x13-inch baking dish, spreading evenly.
For pecan streusel: In a bowl, mix brown sugar, flour, 0.25 cup melted butter, and pecan halves until crumbly. Evenly sprinkle streusel over the casserole. For marshmallow topping, wait to add marshmallows until the last 15 minutes of baking.
Bake for 35 minutes. If adding marshmallows, remove casserole, top with mini marshmallows, and bake for another 10–15 minutes or until golden brown and bubbly around the edges. Let cool slightly before serving.