This sweet potato casserole keeps things straightforward: boiled and mashed sweet potatoes seasoned with butter, cinnamon, and vanilla, topped with mini marshmallows that go golden and gooey in the oven. It serves 8 and takes about an hour start to finish. If you need a crowd-pleasing holiday side that doesn’t require much active effort, this is a reliable one to reach for.
Before you start
The two things that actually affect the final dish are how dry your mashed sweet potatoes are and how evenly you spread them. If the potatoes hold too much water from boiling, the filling turns loose and the marshmallow layer sinks rather than sitting on top — so drain them thoroughly and let them steam off in the colander for a minute or two before mashing. Even spreading matters more than it sounds: a level surface means the marshmallows brown uniformly instead of burning at the thin edges while the thick center stays pale. Use the back of a spoon and take an extra thirty seconds to get it flat.
Common problems and fixes
- Marshmallows slide off or pool to one side: This usually means the filling was too warm when you added the topping. Let the sweet potato layer cool for 5 minutes in the dish before scattering the marshmallows — they’ll grip the surface better.
- Filling tastes flat even though you followed the recipe: Sweet potatoes vary a lot in natural sugar content depending on the variety and how long they’ve been stored. Taste the mash before it goes in the dish and add an extra pinch of salt or a small squeeze of lemon juice — salt does more work here than extra sugar.
- Marshmallows brown in under 10 minutes: Oven hot spots are usually the culprit. Move the dish to the center rack and check it at 15 minutes rather than waiting the full 20. Once marshmallows start browning they go from golden to burnt quickly.
- Edges bubble and overcook while the center is still cold: This happens when the filling goes into the oven straight from the fridge. Bring the assembled dish to room temperature for about 20 minutes before baking so everything heats through at the same rate. Skip the garnish of extra cinnamon on top — it scorches on the marshmallows and isn’t worth the extra dish.
- Casserole is watery after baking: Excess liquid from the sweet potatoes has nowhere to go once the dish is sealed by the marshmallow layer. If you notice the mash looks wet before spreading, stir it over low heat in the pot for 2 to 3 minutes to drive off moisture before transferring to the baking dish.
Make-ahead notes
You can make the sweet potato filling up to 2 days ahead — store it covered in the fridge in the baking dish or in a separate container. When you’re ready to bake, spread it into the greased dish if needed, let it sit at room temperature for 20 minutes, then add the marshmallows and bake as directed. Don’t add the marshmallows ahead of time; they absorb moisture in the fridge and turn sticky and flat. The fully baked casserole keeps in the fridge for up to 3 days. To reheat, cover loosely with foil and warm at 325°F for about 15 minutes — the marshmallow topping won’t look as fresh, but the flavor holds up well. Freezing the baked version isn’t ideal since the marshmallow texture becomes spongy after thawing, but the plain filling freezes fine for up to 1 month.
Sweet Potato Casserole with Marshmallows (Easy Classic)
Equipment
- 9×13 inch (33x23cm) baking dish
- Large Pot
- Colander
- Potato masher
- Large mixing bowl
- Aluminum foil
Ingredients
Sweet Potato Casserole Ingredients
- 4 cups sweet potatoes peeled and cubed, about 2 lbs / 900g
- ½ cup granulated sugar 100g
- 2 tablespoons unsalted butter melted, 1 oz / 28g
- ¼ cup whole milk 60ml
- 1 teaspoon vanilla extract
- ¼ teaspoon ground cinnamon
- ⅛ teaspoon salt
- 8 cups water for boiling, enough to cover sweet potatoes
Topping Ingredients
- 2 cups mini marshmallows about 4 oz / 115g
Instructions
- Preheat your oven to 190°C (375°F). Grease a 9×13-inch (33x23cm) baking dish and set aside.
- Bring a large pot of water to a boil, add the cubed sweet potatoes, and cook for 15-20 minutes or until fork-tender. Drain in a colander and let them steam dry for 1-2 minutes before transferring to a large mixing bowl.4 cups sweet potatoes, 8 cups water
- Using a potato masher, mash the sweet potatoes until smooth. Add sugar, melted butter, milk, vanilla extract, cinnamon, and salt. Stir until well combined and creamy.4 cups sweet potatoes, 1/2 cup granulated sugar, 2 tablespoons unsalted butter, 1/4 cup whole milk, 1 teaspoon vanilla extract, 1/4 teaspoon ground cinnamon, 1/8 teaspoon salt
- Spread the sweet potato mixture evenly into the prepared baking dish.
- Top evenly with mini marshmallows, covering the surface completely.2 cups mini marshmallows
- Bake in the preheated oven for 20-25 minutes until the marshmallows are puffed and golden brown and the edges are bubbling. If the marshmallows start browning too quickly, cover loosely with aluminum foil for the remaining time.2 cups mini marshmallows
Notes
Nutrition
Frequently asked questions
Can I use canned sweet potatoes instead of fresh?
Yes, canned sweet potatoes work, but drain and pat them very dry first or the filling will be too loose. Because canned varieties are often packed in syrup, taste the mash before adding the full amount of sugar and cut back if needed.
Do I have to use mini marshmallows, or can I use regular-sized ones?
Mini marshmallows are strongly preferred here because they cover the surface evenly and melt at a consistent rate. Regular marshmallows can be cut into pieces, but they tend to brown unevenly and leave gaps that expose the filling to direct heat.
How do I know when the casserole is actually done?
The marshmallows should be golden brown on top and the edges of the filling should be visibly bubbling. If the center of the filling still looks cold and the marshmallows are already dark, cover with foil, drop the oven to 350°F, and give it another 5 minutes.
Can I double the recipe for a larger crowd?
Doubling works well — use two 9×13-inch dishes rather than one deeper dish so the filling layer stays thin enough to heat through evenly. Bake time stays roughly the same; just start checking the marshmallows at 18 minutes.
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