Knead the ingredients for the dough and form a roll. Cut into 8 equal parts and roll out each part into equal parts or roll out the entire dough and cut out cookies with a large round cookie cutter. Place half of the cookies on a baking sheet lined with parchment paper and place a teaspoon of apple sauce on each in the center. Brush the edges with egg white and place the counterpart on top and press the edge smooth with a fork. Brush the surface with egg yolk and bake at 180 °C for 15 to 20 minutes. Dust with powdered sugar.