Beat the egg whites with the sugar until foamy and gradually beat in the egg yolks one at a time, Nesquik and soft butter. You get a fluffy foam, to which you then add flour mixed with baking powder.
Layer the prepared dough in an approx. 9 x 13 in' baking sheet greased and sprinkled with flour. Bake in a preheated oven at 355 °F / 180 °C for 18-20 minutes.
Take out the baked dough and turn it upside down. After cooling, cut in half.
Whip the sour cream with the powdered sugar until smooth and layer it on one sheet of dough. Cover with a second sheet.
Let's prepare the glaze. Bring the water and sugar to a boil and add the chocolate broken into pieces. When the chocolate has melted, set aside and add the sour cream. Layer on top and smooth it out nicely.