Nourishing Recipe...

The marshmallows start out firm and matte, then turn glossy and puff up into a soft blanket over the sweet potatoes. That last change is quick enough that I keep an eye on the slow cooker instead of wandering off. Crockpot Sweet Potato Casserole is especially handy when the oven’s busy, but the slow cooker does leave one small detail in your hands: draining the potatoes well before mashing.

I cut the sweet potatoes into even 1-inch cubes so they cook at roughly the same pace, then let them soften in the covered slow cooker. Once they’re tender, butter, milk, brown sugar, vanilla, cinnamon, and salt turn them into a smooth, gently sweet mash. The marshmallows go on at the end, so they melt and puff without spending hours cooking alongside the potatoes. The finished casserole is warm, soft, and topped with a pillowy layer that gives way to every spoonful.

Why Draining the Sweet Potatoes Makes This Slow-Cooker Mash Work

Sweet potatoes release moisture as they cook, and the slow cooker holds onto that steam under its lid. That’s useful while the cubes soften, but the liquid left in the pot isn’t part of the mash. If you leave it there, the butter and milk join an already-wet mixture, and the result can turn loose instead of creamy.

After the potatoes are fork-tender, carefully pour off any water still in the cooker, then return the potatoes to the pot before adding the other ingredients. There’s no need to compensate with extra cooking or more brown sugar; the goal is to remove excess liquid before mashing, not to thicken the casserole afterward. This is also why the potatoes cook with only the measured water rather than sitting submerged. They soften in the covered cooker, and the drained pot gives the finished mash room to hold its shape on the serving spoon.

The mash should look smooth and cohesive once you’ve worked in the butter and milk. If it looks watery, check that no cooking water remains in the pot before you continue. A careful drain gives the sweet potatoes a soft, substantial texture that supports the marshmallow topping instead of letting it slide around.

What the Sweet Potatoes, Brown Sugar, and Marshmallows Each Bring

• Sweet potatoes — Choose firm potatoes without soft or shriveled spots. Peeling and cutting them into even 1-inch cubes helps them soften at a similar rate; much larger pieces may take longer to become easy to pierce. There isn’t a direct substitute that keeps the same sweet-potato flavor and texture.
• Butter and milk — These make the mash creamy and help it turn smooth. Unsalted butter lets the measured kosher salt season the dish without the extra saltiness of salted butter. Use the milk you normally keep on hand; the ingredient list doesn’t specify a particular fat percentage, and replacing both dairy ingredients changes the casserole’s richness.
• Packed light brown sugar — It sweetens the potatoes and brings a mild molasses note. Pack it into the measuring cup so you get the intended amount; a loose scoop can leave the mash less sweet. Dark brown sugar has a stronger molasses taste, so light brown sugar keeps the flavor gentler.
• Vanilla and cinnamon — Vanilla rounds out the sweetness, while cinnamon gives the mash its familiar warm spice. Fresh, fragrant cinnamon is worth using if yours has been in the cabinet for years; if it smells faint, its flavor will be faint, too.
• Miniature marshmallows — Their small size makes it easier to scatter a fairly even layer across the casserole. They melt and puff over the sweet potatoes during the final covered cook. Larger marshmallows won’t cover the surface as evenly without changing how you arrange the topping.

From Tender Cubes to a Puffy Marshmallow Finish

Let the Cubes Soften Under the Lid

Add the peeled, 1-inch sweet potato cubes and water to a 6-quart slow cooker, cover, and cook on LOW for 6 to 7 hours or HIGH for 3 to 4 hours. Keep the lid on during cooking so the slow cooker retains its heat and moisture. The potatoes are ready when a fork pierces them easily, with no firm center resisting the tines. If some pieces are still hard, they need more cooking time before you mash them.

Drain Before You Mash

Carefully drain any water remaining in the slow cooker, then return the potatoes to the pot. Add the butter, milk, packed light brown sugar, vanilla, cinnamon, and kosher salt. Mash until smooth, working through any larger pieces rather than leaving lumps behind. Spread the mixture evenly in the cooker so the topping has a level surface.

Scatter on the Marshmallows

Cover the sweet potatoes with an even layer of miniature marshmallows. Cover the slow cooker again and cook on HIGH for 20 to 30 minutes. The marshmallows should look melted and puffed across the top; if a few areas are still firm, give them more time within that window. Keep the lid closed while they heat so the topping can soften evenly.

Let the Top Set Before Serving

Uncover the slow cooker and let the casserole stand for 10 minutes before serving. That brief pause gives the hot marshmallow topping a chance to settle, so it doesn’t stretch as much when you scoop. Serve from the slow cooker while the sweet potato layer is still warm and soft. The marshmallow top will be tender rather than crisp.

Three Small Changes for a Different Sweet Potato Casserole

Questions That Come Up While Making This Crockpot Casserole

Crockpot Sweet Potato Casserole

Crockpot sweet potato casserole cooks until fork-tender, then gets mashed smooth with butter, milk, brown sugar, and cinnamon. A blanket of miniature marshmallows melts and puffs right in the slow cooker.

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Prep Time 15 minutes mins

Cook Time 7 hours hrs 30 minutes mins

Standing 10 minutes mins

Total Time 7 hours hrs 55 minutes mins

Servings: 8 servings

Course: Side Dish

Cuisine: American

Calories: 326

Ingredients Equipment Method Notes

Ingredients

  

For the sweet potatoes

• 4 lb sweet potatoes peeled and cut into 1-inch cubes
• 0.5 cup water
• 4 tbsp unsalted butter
• 0.25 cup milk
• 0.33 cup light brown sugar packed
• 1 tsp vanilla extract
• 0.5 tsp ground cinnamon
• 0.5 tsp kosher salt

For the topping

• 3 cup marshmallows miniature

Equipment

• 1 6-quart slow cooker

Method

 

Cook the sweet potatoes

1. Add the sweet potatoes and water to a 6-quart slow cooker. Cover and cook on LOW for 6 to 7 hours or HIGH for 3 to 4 hours, until the potatoes are easily pierced with a fork.
2. Carefully drain any remaining water from the slow cooker, then return the potatoes to it.
3. Add the butter, milk, brown sugar, vanilla, cinnamon, and salt; mash until smooth and spread the mixture evenly in the slow cooker.

Add the topping

1. Scatter the marshmallows evenly over the sweet potatoes. Cover and cook on HIGH for 20 to 30 minutes, until the marshmallows are melted and puffed.
2. Uncover and let stand for 10 minutes before serving.

Notes

For the smoothest texture, mash the potatoes thoroughly before adding the marshmallows. Refrigerate leftovers for 3 to 4 days; freeze for up to 2 months. For a dairy-free version, use plant-based butter and milk.