Make the sponge cake: Preheat your oven to 180 degrees Celsius (approximately 356 degrees Fahrenheit). In a large bowl, beat the egg whites while gradually adding the sugar and vanilla sugar until stiff peaks form. Gently fold in the flour and baking powder with a spatula until just combined. Pour the mixture into a greased and floured baking dish (about 30 x 20 cm). Bake for 30 minutes, or until the sponge is golden and a toothpick inserted into the center comes out clean. Allow the sponge to cool slightly. Prepare the milk soak: In a saucepan, heat the 500 ml of milk with 3 tablespoons of sugar until the sugar is dissolved. Do not boil. Pour the warm sweetened milk evenly over the slightly cooled sponge cake. Make the custard filling: In a bowl, whisk the egg yolks with the sugar and vanilla sugar until light and fluffy. Add the flour and cornstarch to the yolk mixture and mix well. Heat the 500 ml of milk in a saucepan to just before boiling, then gradually pour the milk into the yolk mixture, whisking constantly. Return the mixture to the saucepan and cook over medium heat, stirring continuously until the custard thickens. Once thickened, remove from heat and let it cool completely. Beat the margarine (or butter) until creamy, then gradually mix into the cooled custard to form a smooth cream. Assemble the cake: Spread the custard cream over the soaked sponge cake. Top with whipped cream and garnish with grated chocolate. Chill and serve: Refrigerate the cake until set, usually for a few hours. Cut into squares and serve chilled. Enjoy your homemade “Bele Ledene Kocke”! please write an article about this recipe