Put the flour, sugar, vanillin sugar, salt and baking powder into a mixing bowl and mix. Add butter, eggs, almond liqueur and bitter almond flavour and knead with the dough hooks of the hand mixer to a smooth dough. Knead the almonds with your hands. Wrap the dough in foil and chill for about 30 minutes. Form the dough into 5 long rolls (each approx. 4 cm Ø) on a floured work surface.
Place the rolls at a distance on a baking tray lined with baking paper. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 12-15 minutes. Take out and let cool down. Cut rolls diagonally into 1-1.5 cm thick slices. Place the cut surface on the baking tray and roast at the same temperature for another 8-10 minutes.