Sweet Potato Casserole with Marshmallows
The sweet potatoes are ready when a knife slips into the centers without catching, but don’t rush the cooling: peeling them while they’re still too hot is an easy way…
Tip: save now, cook later.The sweet potatoes are ready when a knife slips into the centers without catching, but don’t rush the cooling: peeling them while they’re still too hot is an easy way to burn your fingers. I bake them whole, then mash the soft flesh into this sweet potato casserole with marshmallows for a filling that’s rich without being heavy.
Roasting the potatoes before mixing the filling gives you time to get the marshmallow topping just right, too. The casserole gets its first bake on its own, so the filling can set before the marshmallows go on. That keeps the topping puffy and golden instead of melted into the sweet potatoes.
Kitchen Note
Let the roasted potatoes cool until they’re easy to handle before peeling. The skins slip off more comfortably, and you won’t have to fight hot, steaming potatoes while you’re getting the filling ready.
Save this sweet potato casserole with marshmallows for a holiday table or a cozy supper side—soft, brown-sugar filling under a golden marshmallow top.
Why roasting the sweet potatoes keeps the filling from turning watery
Sweet potatoes bring their own moisture, and boiling them can leave extra water clinging to the flesh. That excess makes it harder for the filling to bake up creamy and hold its shape. Baking them whole keeps the skins around the potatoes as they cook, so there’s no pot of cooking water to drain away or accidentally carry into the mash.
The oven does another useful bit of work: the potatoes soften all the way through while their flavor concentrates. Use the knife test rather than judging by the outside. A potato can look ready and still have a firm center, which leaves stubborn chunks in the filling. Once a knife slides easily into the middle, the flesh is tender enough to mash mostly smooth and combine evenly with the butter, milk, eggs, and brown sugar.
This also gives the casserole its two distinct textures. The filling gets a proper bake before the marshmallows are added, so it sets underneath a topping that stays recognizable. You get creamy sweet potato in each spoonful, not marshmallows dissolved into the surface.
What the sweet potatoes, eggs, and marshmallows each bring
- Sweet potatoes — Choose firm potatoes without soft spots, and scrub them well before baking. Similar-sized potatoes tend to finish closer together. Fresh whole potatoes give you a drier, more consistent mash than canned sweet potatoes, whose packed liquid can make the filling loose.
- Unsalted butter — It adds richness and helps the mash feel smooth. Unsalted butter also lets the kosher salt stay in balance; salted butter can make the finished filling taste too salty unless you adjust the added salt.
- Light brown sugar — Its mild molasses note suits the sweet potatoes without taking over. Dark brown sugar works in the same amount if that’s what you have, though the filling will taste deeper and more caramel-like.
- Whole milk and eggs — Milk loosens the mash, while the eggs help the filling set into a scoopable casserole instead of staying like loose mashed potatoes. Two-percent milk can stand in for whole milk, with a slightly less rich result. Keep the eggs lightly beaten so they blend through the filling without streaks.
- Vanilla extract — It rounds out the brown sugar and sweet potato flavor. Use the extract you keep for baking; there isn’t a close substitute in this short ingredient list.
- Miniature marshmallows — Their small size makes it easy to cover the surface evenly, and they puff quickly in the final bake. If you only have full-sized marshmallows, cut them into smaller pieces so the topping is easier to distribute.
From tender roasted potatoes to a golden marshmallow top
Roast until the centers give way
Heat the oven to 400°F and set the scrubbed sweet potatoes on a rimmed baking sheet. Bake for 45–60 minutes, until a knife slides easily into the centers; the exact time depends on the size of the potatoes. If the knife meets resistance, give them more time rather than trying to mash firm flesh. Let the potatoes cool until they’re easy to handle.
Peel, mash, and mix the filling
Once the potatoes are cool enough to handle, reduce the oven to 350°F and coat a 9×13-inch baking dish with nonstick cooking spray. Peel the potatoes and mash them in a large bowl until mostly smooth. Stir in the melted butter, brown sugar, milk, lightly beaten eggs, vanilla, and kosher salt until the mixture looks even, with no visible streaks of egg. A few small soft pieces are fine; large firm lumps mean the potatoes needed more mashing.
Bake the filling before adding the topping
Spread the mixture in the prepared dish, taking it into the corners so it bakes at an even depth. Bake for 20–25 minutes, until the center reaches 160°F. Don’t judge the middle by the edges alone; the center takes longer to heat through. The first bake gives the egg-enriched filling time to set before the topping goes on.
Toast the marshmallows and let the casserole settle
Scatter the miniature marshmallows evenly over the casserole, then return it to the oven for 5–8 minutes. Watch for marshmallows that have puffed and turned golden; the topping can go from pale to toasted quickly near the end. Let the casserole rest for 10 minutes before serving so the filling settles and scoops more neatly.
Small changes for a less-sweet or marshmallow-free casserole
A less-sweet filling
Leave out the brown sugar and keep the rest of the filling the same. The sweet potatoes will taste more front and center, and the casserole will be less dessert-like; the filling may also be a little less soft.
A marshmallow-free version
Skip the marshmallow topping and serve the baked filling on its own. The casserole will be less sweet and won’t have the soft, toasted cap, but the sweet potato mixture still holds together as a side dish.
Two kinds of servings in one dish
Keep the marshmallows over one half of the casserole so each serving can be topped or plain. The marshmallow layer will be thicker on that side, while the uncovered half stays focused on the buttery sweet potato filling.
Storage and Reheating
- Refrigerator: Store covered for 3–4 days. The marshmallow topping will lose its fresh-baked puff and become softer.
- Freezer: Freeze tightly covered in portions for up to 2 months. Thaw overnight in the refrigerator; the marshmallows may be sticky and won’t regain their original toasted texture.
- Reheating: Warm individual portions in the microwave at medium power in short bursts until hot throughout. Avoid a long, high-power blast, which can make the marshmallows tough before the filling is warm.
Questions that come up when making sweet potato casserole
Sweet Potato Casserole with Marshmallows
Ingredients
Equipment
Method
- Heat the oven to 400°F. Place the sweet potatoes on a rimmed baking sheet and bake for 45-60 minutes, until a knife slides easily into the centers.
- Let the potatoes cool until easy to handle, then reduce the oven to 350°F and coat a 9x13-inch baking dish with nonstick cooking spray.
- Peel the potatoes and mash them in a large bowl until mostly smooth.
- Stir in the melted butter, brown sugar, milk, eggs, vanilla, and salt until evenly combined.
- Spread the mixture in the prepared baking dish and bake for 20-25 minutes, until the center reaches 160°F.
- Scatter the marshmallows evenly over the casserole and bake for 5-8 minutes, until puffed and golden.
- Rest the casserole for 10 minutes before serving.
