Sieve the icing sugar into a mixing bowl. Add flour, salt, vanilla pulp and butter in small pieces. Knead first with the dough hooks of the hand mixer, then with cool hands to a smooth dough
Weigh 500 g dough and wrap in foil. Knead cocoa under the remaining dough (approx. 360 g), also wrap in foil and chill for approx. 1 1/2 hours. Then weigh approx. 100 g light and 125 g dark dough
Roll out the light-coloured dough into a rectangle (4 x 25 cm) on a well floured work surface. Roll out the dark weighed dough into a rectangle (5 x 25 cm) and cut into 5 wide strips (1 x 25 cm). Work accurately, otherwise you will not be able to put it together afterwards. Cut light-coloured dough into 4 wide strips (1 x 25 cm). Chill for about 15 minutes
Lightly whisk the egg whites. Roll out approx. 175 g light-coloured dough on floured foil approx. 2 mm thin and cut straight into a rectangle (approx. 18 x 25 cm). Spread the egg whites on the cold strips and lay them lengthwise in a checkerboard pattern in the middle of the dough sheet (3 strips of dough alternately next to and on top of each other).
Spread the dough sheet with egg white as well and roll the strips firmly into it. Press the edges well together and form a square stick. Chill for about 45 minutes.
Roll out the remaining dough on floured foil to a dark and a light rectangle (approx. 17 x 25 cm). Spread the light-coloured dough thinly with egg white. Place the dark dough exactly on top and roll up carefully from the long side. Chill the roll for about 45 minutes
Cut the well-cooled roll into approx. 0.5 cm wide slices. Place on 2 baking trays lined with baking paper, leaving some space between the biscuits. Bake in the preheated oven one after the other, 2nd shelf from below (electric oven: 175 °C/ convection oven: 150 °C/ gas: stage 2) for 10-12 minutes. Take out of the oven, carefully place on a cake rack and let it cool down
Cut the chessboard roll also into 0.5 cm wide slices, bake as described above and let cool
waiting time approx. 2 1/4 hours