Christmas yams are the dish that divides no one. The sweet potato casserole with marshmallows is an American holiday institution, appearing on tables from Thanksgiving through Christmas dinner without complaint. Despite the name, true yams and sweet potatoes are different vegetables entirely; what gets called "candied yams" in the US is almost always orange-fleshed sweet potatoes, Beauregard or Jewel varieties, baked down until silky and sweet.
The marshmallow topping became standard in the early 20th century, largely credited to a recipe promoted by a marshmallow manufacturer around 1917. It caught on because it works: the marshmallows toast under the broiler into a golden, slightly caramelized layer that contrasts the savory-sweet filling beneath.
This recipe keeps the filling simple and properly spiced with cinnamon, nutmeg, and vanilla, using real butter and brown sugar rather than a sweet potato puree that tastes like baby food. The result is a casserole that holds its shape when scooped and tastes like the holiday side dish people actually look forward to.
Equipment
Instructions
Tap each step to track your progress
- 1
Preheat your oven to 375 degrees F (190 C). Grease a 9x13 inch baking dish with butter or cooking spray.
- 2
Place the peeled, chunked sweet potatoes in a large pot and cover with cold water by 1 inch. Bring to a boil over high heat, then reduce to a steady simmer. Cook until completely tender when pierced with a fork, about 18 to 22 minutes. They should offer zero resistance.
- 3
Drain the cooked sweet potatoes thoroughly and return them to the pot over low heat for 1 to 2 minutes, stirring, to drive off excess moisture. This step keeps the filling from being watery.
- 4
Remove from heat and mash the sweet potatoes until smooth with a potato masher or electric hand mixer. A few small lumps are fine; the filling should look cohesive, not whipped.
- 5
Beat in the softened butter until it melts in completely, then stir in the dark brown sugar, milk, beaten eggs, vanilla extract, cinnamon, nutmeg, and salt. Mix until everything is evenly incorporated and the filling is smooth with a consistent orange color.
- 6
Spread the filling evenly into the prepared baking dish. Smooth the top with a spatula.
- 7
Bake uncovered at 375 F for 25 minutes, until the filling is set through and the edges are just starting to pull away from the dish.
- 8
Remove from the oven and switch it to broil on high. Distribute the mini marshmallows evenly across the entire surface of the casserole in a single layer.
- 9
Return the dish to the oven under the broiler. Broil for 2 to 4 minutes, watching constantly. The marshmallows should puff and turn deep golden brown in spots; pull the dish the moment you see the color you want. They go from golden to burnt in about 45 seconds.
- 10
Let the casserole rest for 5 minutes before serving so the filling firms back up slightly.
Tips & Tricks
Use orange-fleshed sweet potatoes, not white
Beauregard, Jewel, or Garnet varieties have the right moisture content and sweetness for this casserole. White-fleshed sweet potatoes are drier and starchier and don't produce the same silky filling.
Brown sugar, not white
Dark brown sugar has molasses in it, which adds a subtle depth and a touch of bitterness that keeps the casserole from tasting one-dimensionally sweet. Light brown sugar works too but produces a blander result.
Make the filling a day ahead
The sweet potato filling actually improves overnight in the fridge as the flavors settle. Prepare everything through step 6, cover tightly, and refrigerate. On the day, bake from cold (add 5 to 8 minutes to the bake time), then add marshmallows and broil.
Watch the broiler, every second
Mini marshmallows go from pale to perfectly golden to burnt in about 2 minutes total under a hot broiler. Do not leave the kitchen. Pull the dish the moment the color hits deep golden brown.
Salt is not optional
Sweet potato casserole needs the 1/4 tsp of salt in the filling. Without it, the flavors are flat and one-note. Salt sharpens the sweetness and makes the cinnamon read more clearly.
Troubleshooting
The filling is watery or doesn't hold its shape
The sweet potatoes weren't dried out enough after draining. Return drained potatoes to the hot pot over low heat and stir for 1 to 2 minutes before mashing; the steam escaping takes excess water with it. Also make sure you're draining completely and not adding too much milk.
The marshmallows burned before turning golden
Your broiler runs hot, or the dish was too close to the heating element. Move the oven rack down one position and watch the dish the entire time it's under the broiler. The toasting window is narrow; never walk away.
The casserole is too sweet
Dark brown sugar adds depth that cuts through some of the sweetness compared to white sugar. If your sweet potatoes were very large and sweet to begin with, reduce the brown sugar to 1/3 cup. A small pinch of extra salt also brings the flavors into balance.
The filling has a stringy texture
This happens when sweet potatoes are under-cooked before mashing. They need to be completely soft all the way through. If your fork meets any resistance, keep simmering. A hand mixer on low speed for 30 seconds will also smooth out stubborn strings.
The eggs scrambled in the filling
The sweet potato mixture was too hot when the eggs went in. Let the mashed potatoes cool for 5 minutes off the heat before adding the beaten eggs, or temper them by stirring a spoonful of the hot potato mixture into the eggs first, then adding that back to the pot.
Variations
Pecan Streusel Topping
Skip the marshmallows and make a streusel by combining 1/2 cup all-purpose flour, 1/2 cup packed dark brown sugar, 4 tbsp cold unsalted butter (cut into small cubes), and 3/4 cup roughly chopped pecans. Work the butter into the dry ingredients with your fingers until it resembles coarse crumbs, then scatter evenly over the filling before baking. Bake at 375 F for 30 to 35 minutes until the topping is golden and crunchy. This version is less sweet and has a more complex texture.
Vegan Adaptation
Replace the butter with vegan butter (such as Earth Balance) and use full-fat coconut milk instead of whole milk. Substitute the 2 eggs with 2 tablespoons of cornstarch stirred into the milk. The filling will be slightly less creamy but holds together well after baking. Use vegan marshmallows for the topping; they toast similarly to standard ones. Add the vegan:dietary tag if using this variation.
Bourbon Brown Sugar
Add 2 tablespoons of bourbon to the filling along with the vanilla. The alcohol cooks off during baking, leaving a warm, slightly smoky depth that complements the cinnamon well. This version pairs particularly well with the marshmallow topping.
Make-Ahead Sheet Pan Version
Double the recipe and spread into two 9x13 dishes, or spread thinly onto a rimmed baking sheet for a larger batch. The filling bakes faster in a shallower layer; check at 20 minutes. Add marshmallows and broil as directed. Useful for feeding a crowd over 12.
Serving & Gifting
Serve Christmas yams straight from the baking dish while the marshmallow topping is still golden and slightly molten. It pairs well with roast turkey, ham, and classic holiday sides like green bean casserole and cranberry sauce; the sweetness works as a counterpoint to savory mains. For a large Christmas dinner, scoop with a large spoon and keep the rest warm in a low oven (250 F) with foil over the top; remove the foil for the last 5 minutes to refresh the marshmallow layer if needed.
Storage & Freezing
Leftover sweet potato casserole keeps covered in the refrigerator for up to 4 days. Reheat individual portions in the microwave for 1 to 2 minutes, or rewarm the whole dish covered with foil at 325 F for 20 minutes; add fresh marshmallows and broil briefly to restore the topping. The filling freezes well for up to 3 months; freeze without the marshmallow topping, then thaw overnight in the fridge, spread into the baking dish, and add fresh marshmallows before baking.
Common Questions
What is the difference between yams and sweet potatoes?
True yams are a starchy West African tuber with rough brown skin and white or purple flesh. What Americans call "yams" in grocery stores are actually sweet potatoes, specifically orange-fleshed varieties. The labeling confusion dates back to marketing in the mid-20th century. For this recipe, use orange sweet potatoes regardless of how they are labeled.
Can I make sweet potato casserole with marshmallows ahead of time?
Yes. Prepare and bake the filling up to 24 hours in advance, cool completely, and refrigerate covered. On Christmas Day, reheat covered with foil at 325 F for 20 to 25 minutes, then add fresh marshmallows and broil to finish. Do not add the marshmallows before refrigerating or they will dissolve into the filling.
Can I use canned sweet potatoes instead of fresh?
You can, though the texture will be softer and slightly less flavorful. Use 2 cans (about 29 oz each) of canned sweet potatoes packed in light syrup, drained very well. Reduce the brown sugar to 1/4 cup since canned potatoes are often pre-sweetened. Fresh sweet potatoes produce a noticeably better result.
How many sweet potatoes do I need for this casserole?
For 8 servings, you need about 4 pounds of sweet potatoes, which is typically 5 to 6 medium potatoes. A medium sweet potato weighs roughly 5 to 6 ounces. Buy a little extra to account for peeling and trimming.
Is sweet potato casserole gluten-free?
Yes, this recipe as written is naturally gluten-free. The filling contains no flour or wheat products. Check the label on your marshmallows, as some brands contain modified starch that may be wheat-based; most major brands including Jet-Puffed are gluten-free.
Can I use jumbo marshmallows instead of mini?
Mini marshmallows work better because they create a more even, consistently golden layer. Jumbo marshmallows toast unevenly; the tops brown while the bottoms stay raw. If you only have jumbo, cut each one in half with kitchen scissors before laying them out.
