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Sweet Potato Casserole with Marshmallows and Cinnamon Streusel

Sweet potato casserole with marshmallows gets a cinnamon-pecan streusel and a layer of mini marshmallows baked until puffed and lightly golden. The mashed sweet potato filling stays soft beneath the crisp, buttery topping.
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Prep Time 25 minutes
Cook Time 50 minutes
Resting time 10 minutes
Total Time 1 hour 25 minutes
Servings: 12 servings
Course: Side Dish
Cuisine: American
Calories: 393
Ingredients Equipment Method Notes

Ingredients
  

For the sweet potato filling
  • 1 nonstick cooking spray for coating the baking dish
  • 4 lb sweet potatoes peeled and cut into 1-inch cubes
  • water cold; as needed to cover the potatoes by 1 inch
  • 12 tbsp unsalted butter divided (8 tablespoons for the filling and 4 tablespoons cold and cubed for the streusel)
  • 1 cup light brown sugar packed; divided (1/2 cup for the filling and 1/2 cup for the streusel)
  • 0.5 cup whole milk
  • 2 eggs large
  • 1 tsp vanilla extract
  • 0.5 tsp kosher salt
For the cinnamon streusel
  • 0.5 cup all-purpose flour
  • 1 tsp ground cinnamon
  • 0.5 cup pecans chopped
For the marshmallow topping
  • 3 cup mini marshmallows

Equipment

  • 1 9x13-inch baking dish

Method
 

Prepare and cook the sweet potatoes
  1. Heat the oven to 350°F.
  2. Coat a 9x13-inch baking dish with nonstick cooking spray.
  3. Put the sweet potatoes in a 6-quart pot and cover with cold water by 1 inch.
  4. Bring the potatoes to a boil over high heat, then reduce to a simmer and cook for 12–15 minutes, until easily pierced with a fork.
  5. Drain the potatoes well and return them to the pot.
  6. Mash the potatoes with 8 tablespoons of the butter.
  7. Let the mash cool for 5 minutes.
  8. Stir in 1/2 cup of the brown sugar, the milk, eggs, vanilla, and salt until evenly combined.
  9. Spread the mixture in the prepared baking dish.
Make the cinnamon streusel
  1. In a medium bowl, stir together the flour, remaining 1/2 cup brown sugar, cinnamon, and pecans.
  2. Work in the remaining 4 tablespoons cold butter with your fingertips until coarse crumbs form.
Assemble and bake the casserole
  1. Sprinkle the streusel evenly over the sweet potatoes.
  2. Bake for 25–35 minutes, until the center reaches 160°F and the streusel is golden.
  3. Scatter the marshmallows evenly over the casserole.
  4. Bake for 5–8 minutes, until puffed and lightly golden.
  5. Let the casserole rest for 10 minutes before serving.

Notes

For an even streusel, keep the butter cold and work it in just until coarse crumbs form. Refrigerate leftovers for 3–4 days; freezer-friendly. For a dairy-free variation, use plant-based butter and unsweetened non-dairy milk.