Oats in cake? Prepare to have your mind blown. Quick-cooking oats bring a revolutionary delicate crumb to this banana-and blueberry-packed layer cake. For a bright, tangy finish, we blanketed our cake with a smooth Buttermilk Frosting.
Banana-Blueberry Oat Cake
- 1 cup (227 grams) unsalted butter, softened
- 2½ cups (500 grams) granulated sugar
- 4 large eggs (200 grams), room temperature
- 1 tablespoon (13 grams) vanilla extract*
- 2¾ cups (344 grams) plus 1½ tablespoons (12 grams) all-purpose flour, divided
- ¾ cup (68 grams) oat flour
- ⅓ cup (27 grams) quick-cooking oats
- 2 teaspoons (10 grams) baking powder
- 2 teaspoons (10 grams) baking soda
- 1¼ teaspoons (3.75 grams) kosher salt
- ½ teaspoon (1 gram) ground cinnamon
- ¼ teaspoon ground ginger
- 2 cups (472 grams) mashed ripe banana
- 1 cup (240 grams) whole buttermilk, room temperature
- 1½ cups (246 grams) fresh blueberries
- Buttermilk Frosting (recipe follows)
- Garnish: fresh blueberries, banana slices, toasted quick-cooking oats (see Note)
- Preheat oven to 350°F (180°C). Spray 2 (9-inch) round cake pans with baking spray with flour; line bottom of pans with parchment paper.
- In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugar at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition. Beat in vanilla.
- In a large bowl, whisk together 2¾ cups (344 grams) all-purpose flour, oat flour, oats, baking powder, baking soda, salt, cinnamon, and ginger. In a medium bowl, whisk together mashed banana and buttermilk. Add flour mixture to butter mixture alternately with banana mixture, beginning and ending with flour mixture, beating just until combined after each addition.
- In another medium bowl, toss together blueberries and remaining 1½ tablespoons (12 grams) all-purpose flour; fold blueberry mixture into batter until well combined. Divide batter between prepared pans. Tap pans on counter several times to spread batter and release any air bubbles.
- Bake until a wooden pick inserted in center comes out clean, about 50 minutes, rotating pans halfway through baking and loosely covering with foil to prevent excess browning, if necessary. Let cool in pans for 10 minutes; remove from pans, and let cool completely on wire racks.
- Level cake layers, if desired; discard parchment. Place 1 cake layer on a serving plate. Spoon 2½ cups (about 430 grams) Buttermilk Frosting into a large pastry bag fitted with a ½-inch round piping tip (Wilton 1A). Pipe frosting evenly on top of first cake layer; smooth with a small offset spatula. Top with remaining cake layer. Spoon 2½ cups (about 430 grams) frosting into pastry bag, and pipe evenly on top of cake; smooth into an even layer.
- Spoon remaining frosting into pastry bag, and pipe all over sides of cake; holding a bench scraper or a large offset spatula flush against sides of cake, scrape off excess frosting until sides are smooth and layers are somewhat exposed. Pile excess frosting on top of cake; using the back of a spoon or a large offset spatula, spread and swirl frosting as desired. Using a bench scraper or a large offset spatula held flush against cake layers, scrape frosting again to give sides a smooth, finished look. Garnish with blueberries, banana slices, and toasted oats, if desired.
* We used Heilala Vanilla extract
- 2 cups (454 grams) unsalted butter, softened
- ½ teaspoon (1.5 grams) kosher salt
- 2 pounds (907 grams) confectioners’ sugar
- ½ cup (120 grams) whole buttermilk
- 2 teaspoons (8 grams) vanilla extract
- In the bowl of a stand mixer fitted with the paddle attachment, beat butter and salt at medium speed until creamy, about 1 minute, stopping to scrape sides of bowl. With mixer on low speed, gradually add confectioners’ sugar alternately with buttermilk, beginning and ending with confectioners’ sugar, beating just until combined after each addition. Beat in vanilla. Increase mixer speed to medium, and beat until light and fluffy, about 2 minutes, stopping to scrape sides of bowl. Use immediately.