- 1/2 cup (1 stick) unsalted butter melted, plus more for pans
- 2 cups all-purpose flour (spooned and leveled) plus more for pans
- 2 cups packed light-brown sugar
- 2 large eggs
- 2 Granny Smith apples (8 ounces each) peeled and coarsely grated (2 cups)
- 2 Granny Smith apples (8 ounces each) peeled and cut into 1/4-inch dice
- 2 teaspoons baking soda
- 1/2 teaspoons baking powder
- 2 teaspoons ground cinnamon
- 1/2 teaspoon ground ginger
- 3/4 teaspoon salt
- 4 large egg whites
- 1 cup packed light-brown sugar
- 1/4 teaspoon salt
- 1 1/2 cups (3 sticks) unsalted butter room temperature, cut into tablespoons
- Preheat oven to 350. Brush three 8-inch round cake pans with butter; line bottoms with parchment paper rounds. Brush paper with butter, then dust pans with flour (tapping out excess); set aside.
- In a large bowl, whisk together butter, sugar, and eggs until well combined; fold in apples.
- In a medium bowl, whisk together flour, baking soda, baking powder, cinnamon, ginger and salt; add dry ingredients to wet ingredients and mix just until combined. Divide among prepared pans, smooth top.
- Bake until a toothpick inserted in the center of cakes comes out clean, 35 to 45 minutes. Cool 20 minutes in pan, then invert onto cooling racks; peel off parchment. Reinvert cakes and let cool completely, top sides up.
- To ice cake: Place one layer on a serving plate. Spread a quarter of the buttercream over the layer and top with another, then another quarter of the buttercream. Top with third layer and spread remaining buttercream over the top and sides of the cake. Chill at least 1 hour before slicing with a serrated knife.
- Brown Sugar Buttercream: In a heatproof bowl, set over (not in) a pan of simmering water, whisk together egg whites, sugar and salt. Cook, whisking constantly until the sugar has dissolved and the mixture is warm to the touch.
- Transfer to the clean bowl of an electric mixer. Beat on medium speed until fluffy and cooled, about 15 minutes.
- Raise speed to high; beat until stiff peaks form. Reduce speed to medium-low; add butter, 2 to 3 tablespoons at a time, until fully incorporated.
Tips/TechniquesNote: If the mixture seems to have separated after all the butter is incorporated, beat on medium-high until smooth. Reduce speed to low; beat 3 minutes more.