BEFORE BAKING: Grease a baking sheet with 1 Tablespoon solid fat and dust with 2 Tablespoons breadcrumbs. Preheat the oven to
350 °F. Place1 ⅓ stick unsalted butter in a bowl, add ¾ cup granulated sugar, and cream them with a spatula. Then incorporate 4 egg yolks, one at a time. Finally, add 3 cups all-purpose flour combined before with 2 teaspoons baking powder and ⅓ cup milk. Work by hand into a soft, smooth dough.
Separate a third of the dough, wrap it in plastic, and place it in the freezer to firm up.
Press the remaining dough evenly into a thin layer on the bottom of the prepared baking sheet.
Coarsely chop 1 cup walnuts using a large chef's knife.
Peel 5 medium apples, remove the cores, and either slice them thinly or grate them coarsely. If desired, sprinkle them with lemon juice to prevent browning.
Spread the apples evenly over the dough, dust with ½ teaspoon ground cinnamon, 2 Tablespoons granulated sugar, and chopped nuts.
Beat 4 egg whites with ½ cup granulated sugar using a handheld electric mixer with whisk attachement until stiff peaks form. Then, whisk in a tablespoon of wine vinegar. Carefully spread the meringue over the apple layer.
Take the remaining third of the dough out of the freezer and grate it coarsely. Sprinkle the grated dough over the meringue layer. Ensure the dough does not form a thick, impenetrable layer; the meringue should still be visible beneath the grated dough.
Place the cake in the preheated oven and bake for 45 minutes. Let the apple slice cool down and sprinkle with 2 Tablespoons powdered sugar.