Comforting Sweet Potato Casserole with Marshmallows and Oat Streusel — Easy Holiday Side
I like to keep things simple and honest when a dish is this familiar and comforting. Sweet Potato Casserole with Marshmallows and Oat Streusel is one of those recipes that hits the sweet spot between creamy, sweet, and crunchy — and it’s not fussy. The mashed sweet potatoes make a velvety base, the oat streusel gives you that satisfying crisp, and the marshmallows add the nostalgic golden top many of us grew up loving. It’s a reliable side for holiday tables, but just as good when you want something warm and homey on an ordinary night.
Ingredients for this Sweet Potato Casserole with Marshmallows and Oat Streusel
Below are the ingredients I use when I make this recipe. They’re easy to find, and you can tweak a little depending on what you have on hand — like swapping milk for evaporated milk for extra richness, or skipping the nuts if someone in the family has an allergy.
- 3 lb sweet potatoes (about 4 medium), peeled and chopped
- 1/4 cup unsalted butter, melted
- 1/4 cup brown sugar, packed
- 1/4 cup milk (or evaporated milk)
- 1 tsp vanilla extract
- 1/2 tsp ground cinnamon
- 1/4 tsp ground nutmeg (optional)
- 1/4 tsp salt
- 1 cup mini marshmallows
- 3/4 cup old-fashioned rolled oats
- 1/3 cup all-purpose flour
- 1/3 cup brown sugar, packed (for streusel)
- 1/3 cup cold unsalted butter, cubed
- 1/4 tsp ground cinnamon (for streusel)
- 1 tbsp chopped pecans or walnuts (optional)
Instructions
Here’s how I make this casserole. I try to keep steps straightforward and forgiving—this dish is meant to be shared, not micromanaged.
- Preheat the oven to 350°F (175°C) and butter a 9×13-inch baking dish.
- Put the chopped sweet potatoes in a large pot, cover with cold water, add a pinch of salt, and bring to a boil. Lower to a simmer and cook until very tender, about 15–20 minutes. Drain well.
- Mash the sweet potatoes until smooth. Stir in the melted butter, brown sugar, milk, vanilla, cinnamon, nutmeg (if using), and salt. Give it a taste and tweak the sweetness or spice as you like.
- Spoon the mashed sweet potato mixture into the prepared dish and smooth the top with a spatula.
- Make the oat streusel: combine oats, flour, brown sugar, cinnamon and nuts (if using) in a bowl. Cut in the cold butter with a pastry cutter or two forks until you have coarse crumbs; you want a mixture with some pea-sized bits so it gets a nice texture when baked.
- Sprinkle the streusel evenly across the sweet potatoes.
- Bake uncovered for about 20 minutes to set and warm the casserole through.
- Remove the dish and scatter the mini marshmallows over the top. Return to the oven for 5–8 minutes until marshmallows are puffed and lightly golden. If you prefer a deeper toast, pop it under the broiler for 30–60 seconds — but watch it closely; marshmallows brown fast.
- Let the casserole rest for 5 minutes before serving so it holds its shape a little.
That’s it. No tricks, no complicated steps. If you’re making this for a crowd, you can double the recipe and use a larger pan; baking times may increase slightly.
Cook and Prep Times
- Prep time: 15 minutes (peeling/chopping and mashing)
- Cook time: 25–30 minutes (boiling and baking)
- Total time: about 45 minutes
Nutritional information
Nutrition can vary based on exact ingredients and portion sizes, but here’s a general estimate per serving (assuming 8 servings):
- Calories: 420 kcal
- Fat: 16 g
- Carbohydrates: 64 g
- Protein: 3–4 g
- Fiber: 3–4 g
These numbers are approximate — if you need exact figures for dietary reasons, plug your specific brands and amounts into a nutrition calculator.
Frequently asked questions
Can I make this casserole ahead of time?
Yes. You can prepare the sweet potato layer and the streusel a day in advance, cover them separately, and keep them in the refrigerator. When ready to serve, assemble, bake, and add the marshmallows at the end. Alternatively, bake the whole casserole (without marshmallows), cool, and refrigerate. Reheat in a 350°F oven and add marshmallows for the final few minutes.
What can I use instead of marshmallows?
If you’re not a marshmallow fan, you can skip them entirely and just increase the streusel for extra crunch. A sprinkle of toasted coconut can add a different sweetness, or a handful of browned, sweetened pecans gives great texture and nutty flavor.
How do I make the casserole less sweet?
To reduce sweetness, cut back on the brown sugar in the potatoes (or leave it out) and use plain milk instead of sweetened condensed or evaporated milk. You can also use fewer marshmallows or omit them. Add a little extra salt and a squeeze of lemon if you want to brighten the flavor without adding sugar.
One last note: this dish is flexible, which is part of its charm. If you’ve got a little leftover sweet potato, roast it instead of boiling for extra depth of flavor. If you like texture, add more nuts. My family has a lazy Sunday version where I mash on the stove, sprinkle the streusel, and toast the marshmallows with a kitchen torch for a little show-and-tell — and it disappears just as fast. Enjoy, and don’t stress the details. Good food is often simple, warm, and shared.
Sweet Potato Casserole with Marshmallows and Oat Streusel
Ingredients
- 3 lb sweet potatoes (about 4 medium), peeled and chopped
- 1/4 cup unsalted butter, melted
- 1/4 cup brown sugar, packed
- 1/4 cup milk (or evaporated milk for richness)
- 1 tsp vanilla extract
- 1/2 tsp ground cinnamon
- 1/4 tsp ground nutmeg (optional)
- 1/4 tsp salt
- 1 cup mini marshmallows (more for a thicker topping)
- 3/4 cup old-fashioned rolled oats
- 1/3 cup all-purpose flour
- 1/3 cup brown sugar, packed (for streusel)
- 1/3 cup cold unsalted butter, cubed
- 1/4 tsp ground cinnamon (for streusel)
- 1 tbsp chopped pecans or walnuts (optional)
Instructions
- Preheat the oven to 350°F (175°C). Butter a 9x13-inch baking dish or a similarly sized casserole dish.
- Place the chopped sweet potatoes in a large pot and cover with cold water. Add a pinch of salt, bring to a boil, and simmer until tender, about 15–20 minutes. Drain well.
- Mash the sweet potatoes until smooth. Stir in the melted butter, brown sugar, milk, vanilla extract, cinnamon, nutmeg (if using), and salt. Taste and adjust sweetness or spices as needed.
- Spoon the mashed sweet potato mixture into the prepared baking dish, smoothing the top with a spatula so it’s even.
- Make the oat streusel: In a medium bowl combine the rolled oats, flour, brown sugar, cinnamon and chopped nuts (if using). Cut in the cold cubed butter with a pastry cutter or two forks until the mixture resembles coarse crumbs and some small pea-sized pieces remain.
- Sprinkle the oat streusel evenly over the sweet potato layer.
- Bake uncovered in the preheated oven for 20 minutes to set and warm through.
- Remove the casserole from the oven and evenly scatter the mini marshmallows over the top. Return to the oven and bake an additional 5–8 minutes, or until the marshmallows are puffed and golden. Watch closely — they brown fast.
- If you like a deeply toasted top, place the casserole under the broiler for 30–60 seconds, watching constantly to prevent burning.
- Let the casserole rest for 5 minutes before serving so it firms up a bit. Serve warm.
