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Closeup of sweet potato casserole on a white plate.

Sweet Potato Casserole with Marshmallows and Streusel

Mashed sweet potato casserole topped with toasted marshmallows and a brown sugar-cinnamon-pecan streusel. The perfect side dish for Thanksgiving or any other holiday celebration.
Course Side Dish
Cuisine American
Prep Time 20 minutes
Cook Time 40 minutes
Total Time 1 hour 20 minutes
Servings 8 to 10 as a side dish
Calories 260kcal


Mashed sweet potatoes:

  • 3 to 3- ¼ pounds sweet potatoes* peeled and chopped into large chunks, see note
  • 2 tablespoons unsalted butter
  • ¼ cup milk or half and half
  • ½ teaspoon ground cinnamon or pumpkin pie spice
  • 2 tablespoons brown sugar
  • salt to taste


  • 4 tablespoons unsalted butter softened
  • ¼ cup brown sugar
  • ¼ cup all purpose flour for a sturdier streusel add and additional heaping tablespoon of flour
  • ½ teaspoon ground cinnamon
  • teaspoon salt
  • ½ cup chopped pecans
  • 3 cups mini marshmallows or more, if you'd like


Mashed sweet potatoes:

  • Preheat oven to 375°F. Grease a 2 or 2 ½ quart casserole dish (preferably a rectangle or oval so there's a decent surface area for the topping. I use an 8x11) and set aside.
  • Place the sweet potatoes in a large pot, cover with water, and boil until tender (about 7 minutes, depending on the size). Drain really well and return to the pot. Add butter, milk, cinnamon, brown sugar and salt to the potatoes and mash until smooth. Use a hand mixer, if desired, to make them extra smooth. Taste the potatoes and add additional seasonings, if desired.
  • Transfer the mashed potatoes to the prepared casserole dish. Place in the oven until heated through (if they're already warm it will only take a few minutes). While the sweet potatoes are heating, prepare the topping.


  • In a medium bowl, combine butter, brown sugar, flour, cinnamon and salt (I use a fork or rubber spatula to stir and mash the mixture), then mix in pecans.
  • Remove the sweet potatoes from the oven. Top with half the marshmallows, then sprinkle half the streusel over the marshmallows (pinching pieces together with your fingers). Top with the other half of the marshmallows and sprinkle the remaining streusel over the top. Place back into the oven for 8-15 minutes, until the topping is bubbly and golden brown (keep an eye on it so the marshmallows don't burn). You can also place it under the broiler very briefly to add a little more color to the marshmallows. Note: the longer it is in the oven the more likely that the marshmallows will begin to melt. Allow to sit at room temperature for several minutes before serving.



  • You can assemble the cooked and seasoned mashed sweet potatoes in a casserole dish and refrigerate tightly covered for 2 days (without any topping).
  •  You can also prepare the streusel topping (without the marshmallows) and refrigerate that separately.
  • Before serving, bring the streusel topping to room temperature. Heat the potatoes (without any topping) in the oven at 375°F until heated all the way through (30-ish minutes depending on the size of your casserole dish). Or speed it along by microwaving. Once the potatoes are warmed through, sprinkle on the marshmallows and streusel and return to the oven for 8-15 minutes, until the marshmallows are lightly toasted (broil briefly for a darker color).
See tips in the post about using CANNED YAMS.
*Some grocery stores might have these potatoes labeled as YAMS. Make sure you purchase sweet potatoes/yams with orange flesh and pinkish brown skin. Scrape the skin a little to see the color of the flesh, if necessary.


Calories: 260kcal | Carbohydrates: 38g | Protein: 3g | Fat: 11g | Saturated Fat: 4g | Cholesterol: 18mg | Sodium: 109mg | Potassium: 496mg | Fiber: 4g | Sugar: 13g | Vitamin A: 19525IU | Vitamin C: 3.3mg | Calcium: 59mg | Iron: 1.2mg