German Apple Cake (Versunkener Apfelkuchen)

Preheat the oven to 350°F. Grease a kugelhopf or 10-inch Bundt pan.

Sift together the flour, baking powder, and salt. Beat the butter until smooth, about 1 minute. Gradually add the sugar and beat until light and fluffy, about 4 minutes. Beat in the egg yolks, one at a time. Stir in the flour mixture and milk.

Beat the egg whites on low speed until foamy, about 30 seconds. Increase the speed to high and beat until stiff but not dry. Fold one-fourth of the whites into the batter, then gently fold in the remaining whites.

Pour half of the batter into the prepared pan. Spread with half of the apples. Top with the remaining batter, then the remaining apples.

Bake until golden brown, 50 to 60 minutes. Let cool in the pan for 20 minutes, then transfer to a rack and let cool completely.

To make the glaze if using: Combine all the glaze ingredients, stirring until smooth and of pouring consistency. Drizzle over the cake and let stand until set.