Miso Sweet Potato Casserole

Because your Thanksgiving needs a dose of umami

By
Kat Lieu
Kat Lieu, portrait
Kat Lieu
Kat Lieu, formerly a doctor of physical therapy, fell in love with baking and founded a global group, Subtle Asian Baking. She is currently a full-time author and recipe developer at modernasianbaking.com and the best-selling author of Modern Asian Baking at Home. Originally from New York City, she now calls Washington state her home.
Learn about The Spruce Eats' Editorial Process
Updated on 02/13/24
Tested by
Diana Andrews
Headshot of Diana Andrews
Tested by Diana Andrews
Diana earned her B.A. in Fine Art at Queens College and her culinary certification from the Institute of Culinary Education. Diana has served as head recipe developer and editor for Emmy-nominated PBS series Moveable Feast, food editor and test kitchen manager at Fine Cooking Magazine, and recipe developer, and product tester at Food Network.
Learn about The Spruce Eats' Editorial Process
A miso sweet potato casserole in a square baking dish, topped with toasted marshmallows and sesame seeds

The Spruce Eats / Bahareh Niati

Prep: 15 mins
Cook: 60 mins
Freeze: 8 hrs
Total: 9 hrs 15 mins
Servings: 6 servings
Yield: 1 (8x8)-inch

Admittedly, Thanksgiving feels like a dress rehearsal without the show-stopper: a comforting sweet potato casserole. What makes my version steal the limelight? It's the maverick method of freezing those sweet potatoes before roasting. Eyebrows might arch, but once everyone tastes the outcome—a caramelized depth paired with a melt-in-the-mouth velvety softness—they'll be arching for a completely different reason.

Why Is There Miso in My Sweet Potatoes?

But wait, there's another secret weapon here: miso. Ah, miso—my grandfather's gift to me, first introduced through a humble bowl of miso soup. It took a few decades, a venture into founding Subtle Asian Baking, and writing my bestselling cookbook, "Modern Asian Baking at Home," for me to grasp the full magic of this fermented wonder. Pairing miso with sweet might sound as radical as wearing socks with your Crocs, but trust me, it's a game-changer, and it's about to make your sweet potato casserole the talk of the town (or your neighborhood).

How To Make Miso Sweet Potato Casserole

Ready to whip up this dish? It’s like assembling a piece of IKEA furniture, the easy kind though. Just follow the steps (freezing, roasting, mashing, and broiling), but without the leftover mystery screws and bolts. Don’t be surprised when, post-broil, you witness your masterpiece vanish faster than that one pumpkin pie everyone pretends to like.

What To Serve With Miso Sweet Potato Casserole

For those of you juggling menu ideas, imagine this casserole sitting royally beside a perfectly roasted turkey, making your traditional holiday dinner feel like a Michelin-starred global feast. If you're hunting for turkey inspiration, imagine one marinated in soy sauce, garlic, and scallions. Yes, it's a recipe I have up my sleeve and it pairs with this casserole like cookies with milk. Once you've tried this combo, you’ll toast to new traditions and plate-licking revelations!

Tips for Making Miso Sweet Potato Casserole

  • No steam holes needed—There’s no need to use a fork and poke holes all over these potatoes. They will not explode in your oven because the freezing process breaks down the cell walls of the potato, creating tiny holes where steam can escape. 
  • Get thick sweet potatoes—For eating the potatoes on their own, I prefer buying slender and long sweet potatoes; for the casserole, choose the girthier potatoes at the market. They will yield more flesh for the final dish. 
  • For extra smooth sweet potatoes—After peeling the roasted sweet potatoes, transfer the flesh to a food processor and pulse, scraping down the sides a few times, until very smooth. You can also add the miso, butter, and brown sugar at this point and mix them in with the food processor.
  • Garnish with store-bought fried shallots—If you're in a pinch, using store-bought fried shallots or garlic crisps can save time and still add that desired crunchy contrast.
  • Add sugar to taste—You can cut back on or completely omit the brown sugar. The natural sweetness of the potatoes coupled with the miso's depth can be sufficient for many palates.
  • They’re so good you’ll want extra—Bake more sweet potatoes and reserve some for later enjoyment, outside of the casserole. Freeze them again post baking to enjoy as a dessert, my sweet potato freezies. 

Make Ahead

  • The sweet potatoes can be frozen in advance. 
  • You can also bake and mash the sweet potatoes ahead of time and store in the refrigerator for up to two days. Bring to room temperature before adding the marshmallows and broiling the casserole.

"WOW! Freezing sweet potatoes before roasting was an eye-opening experience! And it's true, there's no need to defrost the potatoes; just pop them right into the oven. They were very easy to mash and had a much lighter consistency than traditionally roasted sweets and the addition of miso was magical!" —Diana Andrews

Miso Sweet Potato Casserole/Tester Image
A Note From Our Recipe Tester

Ingredients

  • 6 slender sweet potatoes (8 to 10 ounces each), washed and dried

  • 1 tablespoon miso, red or white

  • 2 tablespoons unsalted butter, softened 

  • Brown sugar to taste, optional 

  • 1 cup mini marshmallows

  • Candied pecans or walnuts, for garnish, optional

  • Cornflakes, for garnish, optional

  • Fried shallots or fried garlic crisps, for garnish, optional

  • Toasted sesame seeds, for garnish, optional 

Steps to Make It

  1. Gather the ingredients.

    Ingredients to make miso sweet potato casserole

    The Spruce Eats / Bahareh Niati

  2. Transfer 6 slender sweet potatoes (8 to 10 ounces each) to the freezer and freeze for at least 8 hours or up to overnight. 

    A baking sheet with 6 frozen sweet potatoes

    The Spruce Eats / Bahareh Niati

  3. Position a rack in the center of the oven and heat to 450 F. Line a baking sheet with foil. Remove the frozen sweet potatoes from the freezer and run them under water. They will be cold, so your numb fingers will be mad at you. 

    A baking sheet of frozen, washed sweet potatoes, and a second baking sheet lined with aluminum foil

    The Spruce Eats / Bahareh Niati

  4. Lay the potatoes on the prepared baking sheet and give each potato some breathing room. Don’t cram them like sardines on the pan. There’s no need to defrost the sweet potatoes. 

    An aluminum-lined baking sheet with six sweet potatoes

    The Spruce Eats / Bahareh Niati

  5. Transfer to the oven and bake until caramelized and somewhat blistered, and the skin easily peels off, 45 to 60 minutes. Halfway through baking, flip the potatoes.

    An aluminum-lined baking sheet with six baked potatoes

    The Spruce Eats / Bahareh Niati

  6. Remove from the oven and allow to cool enough to handle before peeling (they should still be warm). Transfer the sweet potato flesh to a broiler-proof 8 x 8 casserole or baking pan, preferably metal, and mash with a spoon or fork. The flesh will be super soft and easy to mash. 

    A metal, square baking dish with sweet potato being mashed down with a fork

    The Spruce Eats / Bahareh Niati

  7. Mix in 1 tablespoon miso, red or white and 2 tablespoons unsalted butter, softened. Give it a taste to see if you need to add more miso, or to balance the flavor with some brown sugar to taste. Spread the potatoes out in an even layer.

    A square metal baking dish with mashed sweet potatoes topped with butter and red miso, with brown sugar in a small bowl on the side.

    The Spruce Eats / Bahareh Niati

  8. Scatter 1 cup mini marshmallows evenly on top of the mashed sweet potatoes. 

    A square baking dish with mashed miso-sweet potatoes topped with marshmallows

    The Spruce Eats / Bahareh Niati

  9. Heat the oven to broil. Broil the sweet potatoes on the center rack until the tops of the marshmallows are golden brown, a few minutes. Too long and the marshmallows will become burnt. 

    A square baking dish of mashed miso-sweet potatoes topped with browned marshmallows

    The Spruce Eats / Bahareh Niati

  10. Carefully remove the casserole from the oven and garnish with candied pecans or walnuts, cornflakes, fried shallots or fried garlic crisps, and/or toasted sesame seeds. Serve immediately and enjoy!

    A miso sweet potato casserole topped with roasted marshmallows and toasted sesame seeds

    The Spruce Eats / Bahareh Niati

How To Store

Refrigerate leftovers in an airtight container for up to 5 days. Reheat in the microwave or a 350 F oven until heated through. The safe internal temperature for leftovers is 165 F.


If freezing, store in a freezer-safe container or bag, ensuring as much air is removed as possible. It can be frozen for up to a month. To reheat, thaw in the refrigerator and then bake in the oven at 350 F until heated through to 165 F.

Feeling Adventurous? Try This:

  • Make it vegan—For a vegan variation, substitute the butter with a plant-based alternative like vegan butter, coconut oil, or olive oil and use vegan marshmallows (like the ones sold at Trader Joe's).
  • Make it spicy—If you'd like a spicier kick, add a small amount of finely chopped chili or a dash of chili flakes or even a drizzle of chili crisp oil to the sweet potato mash.
  • Use a variety of sweet potatoes—For a more colorful take, try mixing up your sweet potatoes: purple ones, orange yams, and golden Japanese sweet potatoes (satsumaimo).
Nutrition Facts (per serving)
321 Calories
4g Fat
66g Carbs
6g Protein
×
Nutrition Facts
Servings: 6
Amount per serving
Calories 321
% Daily Value*
Total Fat 4g 6%
Saturated Fat 3g 13%
Cholesterol 10mg 3%
Sodium 215mg 9%
Total Carbohydrate 66g 24%
Dietary Fiber 10g 34%
Total Sugars 23g
Protein 6g
Vitamin C 56mg 278%
Calcium 111mg 9%
Iron 2mg 11%
Potassium 1354mg 29%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
(Nutrition information is calculated using an ingredient database and should be considered an estimate.)