Magic Apple Cake

Place sliced apples in a medium microwavable bowl. Cover tightly with plastic wrap and microwave on High until the apples are tender, about 3 minutes. Remove the plastic wrap and let cool slightly, about 10 minutes.

Meanwhile, preheat oven to 325°F. Coat an 8-inch-square baking pan with cooking spray. Line the bottom and 2 sides with parchment paper, leaving a 2-inch overhang on 2 sides; coat the parchment with cooking spray. Arrange the cooled apples in an even layer in the bottom of the prepared pan.

Combine 2 cups milk and the cubed butter in a medium saucepan. Cook over medium-low heat until the butter is melted, about 5 minutes. Do not boil. Remove from the heat and let cool slightly until warm.

Beat 4 egg whites in a large bowl with an electric mixer on medium-high speed until stiff peaks form, about 4 minutes.

In a separate large bowl, combine 4 egg yolks, ¾ cup granulated sugar, 2 teaspoons vanilla, ½ teaspoon cinnamon and ¼ teaspoon salt; beat with the mixer on high speed until pale and creamy, 2 to 3 minutes. Add ⅓ cup all-purpose flour and ⅓ cup whole-wheat flour; beat on low speed until a thick batter forms, about 1 minute.

Gradually add the warm milk mixture to the batter, beating on low speed until fully incorporated, about 1 minute. Let stand for 10 minutes.

Gently fold the beaten egg whites into the batter until mostly incorporated and no large lumps remain. Do not overmix; the batter will be foamy.

Pour the batter over the apples in the prepared pan. Bake until the top is golden, the edges are just pulling away from the sides of the pan, and the center still jiggles slightly, 45 to 50 minutes. Let cool completely in the pan on a wire rack, about 2 hours. Refrigerate until chilled and fully set, at least 1 hour. Using the parchment overhang as handles, lift the cake from the pan. Dust with 1 tablespoon confectioners’ sugar just before serving.