Sweet Potato and Plantain Pie

1 pound (about 1 large) sweet potatoes
vegetable oil, for frying
2-3 very ripe plantains (about 1 cup), peeled and cut crosswise into 1½-inch pieces
1 cup packed light brown sugar
4 ounces (1 stick) unsalted butter, room temperature
2 large eggs, room temperature
1/2 cup evaporated milk
1/2 teaspoon ground cinnamon
1/2 teaspoon ground nutmeg
1/2 teaspoon kosher salt
2 teaspoons vanilla extract
1 (9-inch) pie shell lined with all-butter crust, store-bought or homemade

Adjust an oven rack to the center position and preheat the oven to 400 F.
Wrap the sweet potatoes with foil and place on a baking sheet.
Bake until extremely soft and a knife inserted into each meets no resistance, about 2 hours.
Cool completely, then slice each potato down the center.
Use a spoon to scoop out the potato’s flesh, placing it into a medium bowl.
Using a potato masher, fork or spoon, mash the potatoes until completely creamy and there are no lumps.
Remove any visible fibrous sweet potato strings and discard.
Cover the bowl with plastic wrap and refrigerate for 1 hour.
Meanwhile, fill a Dutch oven with 1½ inches of vegetable oil and warm over medium heat.
Fry the plantains, in batches, until golden-brown on each side, about 4 minutes.
Transfer the plantains to a paper towel-lined plate. Remove from the oil; drain excess oil on a paper towel.
Add the plantains to the bowl with the mashed sweet potatoes and puree using an immersion blender, until smooth.
Cover the bowl with plastic wrap and refrigerate until completely chilled, about 1 hour.
Reduce the oven temperature to 350 F.
Using a hand mixer or a standing mixer with a paddle attachment, cream the brown sugar and butter on medium speed until light and fluffy, about 3 minutes. Add the eggs and mix until well-blended.
With the mixer on, slowly pour in the evaporated milk and mix until well-combined. Add the cinnamon, nutmeg, salt and vanilla extract, and mix to combine. Add 2 cups worth of the pureed sweet potatoes and plantains, and beat until the filling shows small white specks, about 1 minute.
Pour the mixture into the pie shell and bake on the middle rack of the oven until the top of the filling slightly browns and has a caramelized shine, about 1 hour and 15 minutes.
Remove the pie from the oven and allow it to cool at room temperature for 1 hour before serving.

Note
Sweet potato is cooked all the way through when you’re able to easily stick a knife through it. When mashing your potatoes, discard of the “strings” and fibers that may stick to the paddle attachment or potato masher.