Cook 1½ lb. sweet potatoes (about 4 medium), scrubbed, in a medium pot of boiling water, stirring occasionally, until a tester inserted into centers meets no resistance, 40–45 minutes. Drain and let sit until cool enough to handle. Remove skins, transfer flesh to a medium bowl, and mash with a potato masher or fork. Let cool.
Preheat oven to 350°. Spray three 9″-diameter cake pans with nonstick vegetable oil spray, then line bottoms with parchment paper rounds. Spray parchment and dust pans with cake flour, tapping out excess.
Sift 3¼ cups (374 g) cake flour, 2 tsp. baking powder, 1½ tsp. ground cinnamon, 1 tsp. ground nutmeg, and ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt into a large bowl (or just whisk to remove lumps). Combine 1½ cups (300 g) granulated sugar, 1½ cups (packed; 300 g) light brown sugar, ½ cup (1 stick) unsalted butter, melted, slightly cooled, 7 Tbsp. vegetable oil, and 1 Tbsp. vanilla extract in the bowl of a stand mixer fitted with the paddle attachment. Beat on medium-high speed until light, fluffy, and no lumps remain, about 5 minutes.
Add 5 large eggs, room temperature, to sweet potato purée and mix well. Scrape into sugar mixture and beat to combine, scraping down bowl as needed. Reduce speed to low and with motor running, gradually add dry ingredients; mix just until incorporated. Divide batter evenly among prepared pans. Bake until cakes are slightly risen, tops are set, and a tester inserted into the centers comes out clean, 25–30 minutes.
Transfer pans to a wire rack and let cakes cool in pans 5 minutes. Run a small knife around edges of cakes and turn out onto racks. Remove parchment and let cool completely (rounded side down). Tightly wrap cakes individually in plastic and freeze until thoroughly chilled (this will make cakes easier to frost), about 2 hours.
Frosting and assembly
Beat 2 16-oz. packages full-fat cream cheese, room temperature and 1 cup (2 sticks) salted butter, room temperature in the bowl of a stand mixer fitted with paddle attachment on high speed until smooth and creamy, about 1 minute. Add 8 cups (906 g) powdered sugar, sifted or whisked to remove lumps, 1 Tbsp. vanilla extract, and ¾ tsp. Diamond Crystal or ½ tsp. Morton kosher salt and beat on low speed 30 seconds (place a kitchen towel over bowl to capture any puffs of sugar). Increase speed to high and beat frosting 2 minutes. It should be thick and creamy.
Place a cake, right side up, on a large plate or cake stand. Spread one third of frosting on top. Set another cake on top and frost with half of remaining frosting. Repeat process with remaining cake and frosting. For the cleanest slices, chill 3 hours before slicing. Top with long orange zest strips (if using) just before serving.
Editor’s note: This sweet potato cake recipe was first printed in our November 2020 issue. Looking for more sweet potato recipes? Check out our favorites like a savory sweet potato casserole with brown butter, a sweet potato and blue cheese dip, and a sweet potato pie with marshmallow whip.