Loading…

When the mini marshmallows puff and turn golden, the sweet potato layer underneath should already be set, not still loose in the middle. Baking the filling first gives it time to cook through before the topping gets its short toast in the oven. That timing is what makes this Sweet Potato Casserole with Marshmallows easy to portion instead of serving as a warm scoop.

I boil the sweet potatoes until a fork slides through easily, then mash them smooth while they’re still warm. Brown sugar, butter, milk, eggs, vanilla, and cinnamon turn that mash into a soft, lightly spiced filling. A blanket of mini marshmallows finishes each bite with a browned, pillowy top and a sweet contrast to the potatoes.

Why the Marshmallows Wait Until the Sweet Potato Filling Sets

The filling has eggs in it, so it needs its own bake before the marshmallows go on. That first stretch in the oven cooks the egg mixture through and gives the soft mash a chance to hold together. I bake until the center reaches 160°F, then add the topping. Putting marshmallows on at the beginning would leave them in the oven much longer, making it harder to get a soft, puffed layer with an evenly browned surface.

Think of the topping as a quick finish, not a lid that needs to cook along with the potatoes. Once it’s scattered across the warm filling, the marshmallows need only 8 to 12 minutes to puff and turn golden. Keep an eye on them near the end: the change from pale to toasted happens quickly. The casserole rests briefly after baking, which gives the filling a little time to settle before you serve it.

What the Sweet Potatoes, Eggs, and Marshmallows Each Bring

• Sweet potatoes — Fresh sweet potatoes give you control over the filling’s moisture because you boil the peeled chunks and drain them before mashing. Choose firm potatoes without soft spots. Canned sweet potatoes aren’t a direct swap here; they’re already cooked and may come packed with liquid or syrup.
• Eggs — Lightly beaten eggs help the filling set as it bakes, so the casserole is soft but not just loose mashed potatoes. Keep them in the mixture if you want the same texture; leaving them out changes how the center holds together.
• Butter and whole milk — Unsalted butter adds richness without bringing extra salt, and whole milk loosens the mash while keeping it creamy. For a dairy-free version, use unsalted plant-based butter and unsweetened oat milk in their place; the filling will taste a little less buttery.
• Light brown sugar — Its mild molasses note fits the sweet potatoes without taking over. Dark brown sugar works in its place in the same measure, with a deeper molasses flavor.
• Vanilla and cinnamon — These round out the sweetness with warmth. Regular grocery-store vanilla and ground cinnamon work well, so there’s no need to seek out specialty versions.
• Mini marshmallows — Their small size makes it easier to scatter a consistent layer from edge to edge. If you only have large marshmallows, cut them into smaller pieces so they cover the filling more evenly.

From Fork-Tender Potatoes to a Toasted Marshmallow Top

Simmer the Sweet Potatoes Until a Fork Slides In

Heat the oven to 350°F and grease a 9×13-inch baking dish with the softened tablespoon of butter. Put the peeled, 1-inch sweet potato chunks and water in a 6-quart pot, bring the water to a boil over high heat, then lower the heat to simmer. Cook for 15 to 20 minutes, until the largest chunks are easily pierced with a fork. Drain the potatoes well; leftover water can make the filling looser than you want.

Mash Smooth, Then Mix in the Filling Ingredients

Return the drained sweet potatoes to the pot and mash until smooth. Stir in the melted butter, brown sugar, milk, lightly beaten eggs, vanilla, cinnamon, and kosher salt until everything is combined. Scrape the bottom and sides of the pot as you mix so you don’t leave pockets of plain potato or streaks of seasoning. The mixture should look even before it goes into the baking dish.

Bake the Filling Before Adding the Topping

Spread the filling in the prepared dish, taking it all the way into the corners so it bakes in an even layer. Bake for 20 to 25 minutes, until the center reaches 160°F. Don’t judge the center only by the edges, which heat first; check the middle with an instant-read thermometer. If it hasn’t reached 160°F, give it a little more time before moving on.

Toast the Marshmallows and Let the Casserole Rest

Scatter the mini marshmallows evenly over the baked filling. Return the dish to the oven for 8 to 12 minutes, watching for marshmallows that are puffed and golden brown rather than dark. Let the casserole rest for 10 minutes before serving. That short pause makes it easier to lift portions without the filling immediately spreading across the plate.

Three Easy Ways to Adjust the Sweetness and Flavor

Questions About Making Sweet Potato Casserole with Marshmallows

Sweet Potato Casserole with Marshmallows

Sweet potato casserole with marshmallows is baked in a 9x13-inch dish until the filling is set and the marshmallow topping is puffed and golden brown. Sweet potatoes, brown sugar, cinnamon, and vanilla make a smooth, warmly spiced filling.

Print Recipe Pin Recipe

Prep Time 15 minutes mins

Cook Time 50 minutes mins

resting 10 minutes mins

Total Time 1 hour hr 15 minutes mins

Servings: 10 servings

Course: Side Dish

Cuisine: American

Calories: 320

Ingredients Equipment Method Notes

Ingredients

  

For the sweet potato filling

• 5 tbsp unsalted butter divided (1 tablespoon softened and 4 tablespoons melted)
• 3 lb sweet potatoes peeled and cut into 1-inch chunks
• 8 cup water
• 0.5 cup light brown sugar packed
• 0.33 cup whole milk
• 2 eggs large, lightly beaten
• 1 tsp vanilla extract
• 0.5 tsp ground cinnamon
• 0.5 tsp kosher salt

For the topping

• 1 bag (10 oz) mini marshmallows

Equipment

• 1 9x13-inch baking dish

Method

 

Prepare the sweet potato filling

1. Heat the oven to 350°F.
2. Grease a 9x13-inch baking dish with 1 tablespoon softened butter.
3. Put the sweet potatoes and water in a 6-quart pot and bring to a boil over high heat.
4. Reduce the heat and simmer for 15 to 20 minutes, until the chunks are easily pierced with a fork.
5. Drain the sweet potatoes well.
6. Return the sweet potatoes to the pot and mash until smooth.
7. Stir in the remaining 4 tablespoons melted butter, brown sugar, milk, eggs, vanilla, cinnamon, and salt until combined.
8. Spread the mixture in the prepared baking dish.
9. Bake for 20 to 25 minutes, until the center reaches 160°F.

Add the marshmallow topping

1. Scatter the marshmallows evenly over the casserole.
2. Bake for 8 to 12 minutes, until puffed and golden brown.
3. Let the casserole rest for 10 minutes before serving.

Notes

For the smoothest filling, mash the sweet potatoes until no chunks remain. Refrigerate leftovers for 3 to 4 days; freezing is suitable. For a dairy-free swap, use plant-based butter and unsweetened non-dairy milk.