It's Monday, November 17th, and I'm writing this from a chilly evening in Casablanca, Morocco. My kitchen is thousands of miles from my home in Austin, Texas, but my mind is 100% on Thanksgiving. For my family, it is not Thanksgiving without this exact dish. This isn't just Sweet Potato Casserole; it's the ultimate, decadent, over-the-top version. It's a creamy, rich, spiced sweet potato base, topped with both a crunchy, buttery pecan streusel and a gooey, golden-brown layer of toasted marshmallows. It is the king of holiday side dishes, and this is the only recipe you'll ever need.
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My non-negotiable tip: You must bake the casserole with the streusel first, and then add the marshmallows only for the last 5-10 minutes. On my first test years ago, I put the marshmallows on for the full 25 minutes, and they dissolved into a burnt, sugary, weeping mess. The final broil is the secret to a perfect, toasty top.
The Perfect Holiday Casserole
This recipe is pure, nostalgic comfort. It's a classic Southern-style casserole, which means it's rich, sweet, and decadent enough to almost be a dessert. The base isn't just "mashed potatoes;" it's a rich, smooth custard made by mashing the sweet potatoes with eggs, butter, milk, and brown sugar. This bakes into a firm-yet-creamy "soufflé" that is the perfect foundation for the two distinct, delicious toppings.
Why You'll Love This Recipe
- The Best of Both Worlds: You don't have to choose! This recipe has both the crunchy, buttery pecan streusel and the classic, gooey, toasted marshmallow topping.
- Incredibly Rich & Creamy: The filling is a rich, soufflé-like custard, not just plain mashed potatoes.
- The Ultimate Holiday Side: This is the show-stopping, crowd-pleasing side dish that everyone looks for at Thanksgiving and Christmas.
- Perfect for Making Ahead: You can assemble the entire casserole (minus the marshmallows) a day in advance, making your holiday so much less stressful.
Ingredients
Here's what you'll need for this decadent holiday classic. For the full list with precise measurements, see the recipe card at the end of the post!
For the Sweet Potato Filling
- Sweet Potatoes: 5 large sweet potatoes (about 8 cups cubed). I prefer the orange-fleshed Garnet or Jewel varieties.
- Eggs: 4 large eggs, at room temperature. This is what makes it a "soufflé."
- Butter: 1 stick of unsalted butter, melted.
- Milk: Whole milk (or half-and-half) for richness.
- Sugar: Packed dark brown sugar for that deep, molasses flavour.
- Flavour: Pure vanilla extract and kosher salt.
For the Streusel & Topping
- Brown Sugar: Packed dark brown sugar.
- Flour: All-purpose flour.
- Butter: Unsalted butter, melted.
- Pecans: Chopped raw pecans.
- Marshmallows: 2 ½ cups of mini marshmallows.
How to Make Sweet Potato Casserole with Marshmallows
This is a simple "boil, mash, top, and bake" recipe.
Step 1: Preheat and Cook the Sweet Potatoes
First, I preheat my oven to 350°F (175°C).
I place the peeled, cubed sweet potatoes in a large pot and cover them with cold, salted water. I bring them to a boil, then reduce the heat to a simmer and cook for about 15 minutes, or until they are completely fork-tender. I drain them very well and return the hot potatoes to the pot.
Step 2: Make the Sweet Potato Filling
To the pot with the hot, drained potatoes, I add the 4 large eggs, 1 stick of melted butter, the whole milk, ½ cup of dark brown sugar, the vanilla, and the salt.
I use a potato masher or a fork to mash everything together until it's mostly combined. A few small lumps are perfectly fine and add to the rustic, homemade texture. I transfer this mixture to a large 9x13 inch baking dish and spread it into an even layer.
Step 3: Make and Layer the Streusel Topping
In a medium bowl, I mix the 1 cup of dark brown sugar and the ½ cup of all-purpose flour. I pour in the 4 tablespoons of melted butter and stir with a fork until large, crumbly clumps form.
I stir in the chopped pecans. I sprinkle this streusel mixture evenly all over the sweet potato base.
Step 4: Bake, Top with Marshmallows, and Bake Again
I bake the casserole (with just the streusel) for 25 minutes, or until the filling is hot and the streusel is lightly toasted.
Now, for the finale: I remove the casserole from the oven and scatter the mini marshmallows evenly over the hot streusel. I place it back in the oven and bake for another 5-10 minutes. I watch it like a hawk during this stage! The marshmallows will puff up and turn a perfect, golden-brown.
Common Mistakes to Avoid
- Over-Baking the Marshmallows: This is the #1 mistake. If you put the marshmallows on for the full 30-minute bake, they will melt, dissolve, and then burn into a sticky, black mess. They are a topping, added only for the last 5-10 minutes.
- Using Watery Potatoes: You must drain your boiled potatoes very, very well. If you transfer them to the bowl with a lot of water, your casserole will be soupy.
- Baking vs. Roasting: Boiling the potatoes (as this recipe calls for) is fast and easy. However, you can also roast the sweet potatoes whole (like in my Twice-Baked Sweet Potato recipe) for a deeper, more caramelized flavour.
Tips and Tricks for Success
- Don't Use a Mixer: Do not use a stand mixer or electric mixer to mash the sweet potato filling. Beating the starchy potatoes will turn them into a gummy, gluey paste. A simple hand-held potato masher or even a large fork is all you need.
- The Two-Topping Dream: This is the best part! The streusel layer bakes into the potato custard a bit, and the marshmallow layer toasts on top. It's the perfect combination of crunchy, gooey, and creamy.
- Toast Your Pecans: For an even deeper, nuttier flavour, toast your chopped pecans in a dry skillet over medium heat for 3-5 minutes until fragrant before you add them to the streusel mix.
- The Broiler Trick: If your marshmallows aren't browning as fast as you'd like, you can switch the oven to the broiler setting for the last 1-2 minutes. But do not walk away-they will go from golden to black in 15 seconds!
Variations
This is a classic, but you can always add your own family's twist!
- Just Streusel (No Marshmallows): This is a classic "Sweet Potato Soufflé." Just bake the casserole with the streusel topping for 30-35 minutes until hot and bubbly.
- Just Marshmallows (No Streusel): For the "kid-friendly" classic, bake the filling for 20-25 minutes without the streusel, then top with the marshmallows and bake for the final 5-10 minutes.
- Add Spices: The recipe is simple, but you can add 1 teaspoon of ground cinnamon and ½ teaspoon of ground nutmeg to the sweet potato filling (Step 2) for a spicier, more "pumpkin-pie-like" flavour.
How to Serve
This Sweet Potato Casserole is the king of the Thanksgiving side dishes.
- It's the perfect, sweet, and savory companion to Roast Turkey, Baked Ham, and salty, savory Green Bean Casserole.
- Serve it hot, straight from the oven, in its 9x13 dish.
- I always serve it with the main meal, but let's be honest-it's also the best dessert.
Make Ahead and Storage
This is one of the best make-ahead dishes for the holidays!
- Make Ahead: This is my #1 holiday hack. You can assemble the entire casserole (the sweet potato filling and the streusel topping) in the baking dish, then cover it tightly and refrigerate it unbaked for up to 2 days.
- Baking from Cold: When ready to bake, let it sit on the counter while the oven preheats. Bake at 350°F (175°C), covered with foil, for 30-40 minutes (since it's cold), then remove the foil, top with the marshmallows, and bake for the final 5-10 minutes.
- Storage: Store leftovers, covered, in the refrigerator for up to 4 days.
- Reheating: Reheat in a 350°F (175°C) oven for 15-20 minutes, or in the microwave. The marshmallows will re-melt and be delicious!
Recipe Notes / What I Learned
This recipe is a hybrid of two classic versions: the crunchy pecan-topped soufflé and the gooey marshmallow-topped casserole. By combining them, you get the best of both worlds. The pecans in the streusel add a necessary, nutty crunch that cuts through all the sweet, creamy, and gooey textures. It's a perfect, balanced bite every single time.
Nutrition Snapshot
Estimated Nutrition Per Serving (1/12th of casserole): ~420 calories · 5g protein · 62g carbs · 18g fat (This is an approximation for a very decadent side dish and can vary based on your specific ingredients.)
Sweet Potato Casserole With Marshmallows
Equipment
- Large pot
- Large bowl
- Potato masher or fork
- 13" x 9" baking dish
- Medium bowl
Ingredients
Group: Potatoes
- 5 large sweet potatoes, peeled, cubed (about 8 c.)
- 4 large eggs
- ½ cup unsalted butter, melted (1 stick)
- 1 cup whole milk
- ½ cup packed dark brown sugar (110 g.)
- 2 tsp. pure vanilla extract
- 1 tsp. kosher salt
Group: Streusel Topping & Assembly
- 1 cup packed dark brown sugar (215 g.)
- ½ cup all-purpose flour (60 g.)
- 4 Tbsp. unsalted butter, melted (½ stick)
- 1 cup chopped raw pecans
- 2 ½ cups mini marshmallows
Instructions
- Preheat oven to 350°. Place potatoes in a large pot and cover with water. Bring to a boil, then reduce heat to medium-low and simmer until potatoes are fork-tender, about 15 minutes. Drain and let cool slightly.
- Transfer potatoes to a large bowl. Add eggs, ½ cup melted butter, milk, ½ cup brown sugar, vanilla, and salt. Using a potato masher or fork, mash potatoes until combined. Transfer to a 13" x 9" baking dish.
- In a medium bowl, mix 1 cup brown sugar, flour, and 4 Tbsp. melted butter until clumps form. Stir in pecans, then spread over potatoes. Top with marshmallows.
- Bake casserole until cooked through and marshmallows are golden brown, about 25 minutes.
Nutrition
FAQs
Can I use fresh sweet potatoes instead of boiling?
Yes! You can roast 5 large sweet potatoes (pricked with a fork) at 400°F (200°C) for 45-60 minutes until very tender. Let them cool, then scoop the flesh out. This will give you a deeper, more caramelized flavour.
Can I make this dairy-free?
Yes. Use a plant-based butter (like Miyoko's Kitchen) and a plant-based milk (like full-fat oat milk or unsweetened almond milk). Most mini-marshmallows are naturally dairy-free (but check for gelatin if vegan!).
Can I make this gluten-free?
Easily! The filling is naturally gluten-free. Just substitute the ½ cup of all-purpose flour in the streusel with a 1-to-1 gluten-free baking blend.
