Purple Sweet Potato Casserole with Homemade Cinnamon Marshmallow Meringue
A striking twist on the holiday classic! The deep violet mash of purple sweet potatoes meets a homemade cinnamon marshmallow meringue that’s whipped until glossy and toasted until golden. Vegetarian-friendly and refined sugar–free, it’s the kind of side that doubles as dessert and steals the show either way.
Equipment
- 8x8 or similar baking dish
- Saucepan
- Stand mixer or hand mixer
- Candy thermometer
- Mixing bowls
- Kitchen torch
Ingredients
For the Sweet Potato Base
- 2 lbs purple sweet potatoes peeled and cubed
- ¼ cup whole milk or half-and-half
- 3 tbsp pure maple syrup
- 1-2 tbsp unsalted butter softened
- 1 tsp pure vanilla extract
- ½ tsp cinnamon
- ¼ tsp nutmeg
- Pinch of sea salt
For the Homemade Marshmallow Fluff
- ¾ cup granulated sugar
- ¼ cup pure maple syrup or honey
- ¼ cup water
- 3 large egg whites room temperature
- ¼ tsp cream of tartar
- ½ tsp ground cinnamon
- 1 tsp vanilla extract
- Pinch of salt
Instructions
- Add cubed purple sweet potatoes to a pot of salted water. Boil for 15–20 minutes until tender. Drain and let cool slightly.
- In a large bowl, mash the potatoes until smooth. Stir in milk, maple syrup, butter, vanilla, cinnamon, nutmeg, and salt. Blend until creamy and cohesive.
- Preheat oven to 350°F (175°C). Transfer the mash into a greased baking dish. Smooth the surface with a spatula and bake uncovered for 25 minutes.
- In a small saucepan, combine sugar, maple syrup (or honey), and water. Heat over medium until the mixture reaches 240°F (soft-ball stage) on a candy thermometer.
- While it heats, beat egg whites, cream of tartar, and salt in a stand mixer on medium-high until soft peaks form.
- With the mixer running, slowly stream in the hot syrup. Continue whipping for 5–7 minutes, until thick, glossy peaks form. Add cinnamon and vanilla; beat 30 seconds more.
- Spoon the fluff over the baked casserole, forming peaks with the back of a spoon. Use a kitchen torch to toast until golden brown on the tips.
- Let it sit for about 10 minutes before serving so the layers can settle slightly.
Notes
The syrup needs to hit exactly 240°F to create the right structure; lower temperatures will make it soft, higher will make it grainy. Make sure to keep an eye out on the temperature of your hot syrup!
Purple sweet potatoes can vary in sweetness. Taste after boiling/cooling and adjust with a bit more maple syrup if needed.
If you don’t have a torch, use the broiler on low and watch closely. The marshmallow meringue can also toast up beautifully this way :)