This custard is made a lot like the filling for pumpkin pie, but with mashed sweet potatoes. Then the whole thing is topped with toasted molasses marshmallow. For an easier pie, you can swap the marshmallow for meringue or just plenty of whipped cream.
Makes one 9-inch single-crust pie
Difficulty: Hard
Make Ahead and Storage: The pie can be made up to 1 day ahead, but it’s best to add the topping the same day you serve it. The finished pie can be stored, loosely covered, at room temperature for up to 3 days.
1. Preheat the oven to 375°F / 190°C, preferably with a baking stone on the bottom rack.
2. Make the filling: In a large bowl, whisk together the eggs and both sugars until well combined, about 1 minute. Add the vanilla, melted butter, and cream and whisk to combine. Add the sweet potatoes and whisk until combined—the mixture should be relatively smooth. Stir in the spices.
3. Pour the filling into the piecrust, smoothing it into an even layer.
4. Bake the pie on the stone or bottom rack until the filling is set at the edges but still slightly jiggly in the center, 40 to 45 minutes. Cool completely.
5. Make the marshmallow topping: Pour 81 g / ⅓ cup of the water into a small heatproof bowl, and sprinkle the gelatin over it. Let soak for at least 5 minutes. Grease a silicone spatula and an offset spatula with nonstick spray; set aside.
6. Meanwhile, combine the remaining 81 g / ⅓ cup water, the granulated sugar, molasses, and corn syrup in a medium saucepan and bring the mixture to a boil over medium-high heat. You can stir the mixture before it comes to a boil to help dissolve the sugar, but stop stirring the moment it starts to boil. Attach a candy thermometer to the side of the pan (or have an instant-read thermometer ready). Boil the mixture until it registers 240°F / 115°C.
7. Meanwhile, place the egg whites in the bowl of a stand mixer fitted with the whisk attachment (or use a large bowl and a hand mixer) and whip on low speed until lightly frothy. Melt the gelatin over a water bath (or in a heatproof bowl set over a pan of boiling water) or in the microwave, about 30 seconds.
8. When the sugar mixture registers 240°F / 115°C, increase the mixer speed to medium-high and add the syrup to the bowl in a slow, steady stream. Pour in the melted gelatin with the mixer running and whip on high speed until the mixture is bright white, fluffy, and aerated and holds medium peaks, 4 to 5 minutes.
9. Use the greased spatula to transfer the molasses marshmallow to the top of the cooled pie. Working quickly, use the spatula to spread the marshmallow over the filling, making lots of peaks and valleys.
10. Let the marshmallow topping set for 5 minutes, then use a kitchen torch to toast the surface. Yes, you can skip this step, but it looks cool and tastes all campfire-y.
✻ Why It Works
Sweet potatoes make an excellent base for a custard pie, and while these pies are often compared to pumpkin pies, there’s an important difference. Sweet potatoes have a higher level of starch than pumpkin does, so it’s important not to overmash them, which can make them gluey. I like my sweet potato pie a bit rustic—I just use a fork to coarsely mash the potatoes while they’re hot. If you want your filling a bit smoother, use a potato masher or a food mill.
★ Pro Tip
The marshmallow layer is easier to slice through if you spray your knife (and pie server) with nonstick spray before you cut.