Mix flour and baking powder and sieve into a bowl. Spread butter in small pieces on top. Add sugar, vanillin sugar, salt and egg yolk. Knead first with the dough hooks of the hand mixer, then with cool hands to a smooth shortcrust pastry. Halve the dough.
Roll out one half of the dough to a rectangle (25 x 30 cm) on the floured work surface. Spread half of the cranberries on top, leaving a 1 cm wide edge all around. Roll up the dough from the long side. Place the roll on a board, cover with cling film and chill for about 1 hour. Process the remaining dough and cranberries in the same way. Whisk egg white and 1 teaspoon of water. Spread a roll of dough with whisked egg white, first sprinkle with decorating sugar, then with poppy seeds and press down lightly. Cut the roll with a saw knife into 1 cm wide slices and place them on a baking tray covered with baking paper. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 10 minutes.
Whisk egg white and 1 teaspoon of water. Spread a roll of dough with whisked egg white, first sprinkle with decorating sugar, then with poppy seeds and press down lightly. Cut the roll with a saw knife into 1 cm wide slices and place them on a baking tray covered with baking paper. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 10 minutes. Process the second roll with the remaining ingredients in the same way and bake in the same way on a second baking tray lined with baking paper. Let the cranberry-poppy seed rolls cool on a cake rack
waiting time approx. 1 1/2 hours