Cream fat, sugar and salt. Stir in eggs one after the other. Mix flour and baking powder. Alternately stir buttermilk and flour mixture into the egg mixture. Halve the dough. Mix 1 half with red fruit jelly powder, the other half with custard powder. Grease a baking tray (37 x 32 cm).
Pour the vanilla dough into a piping bag with a large perforated spout. Spray strips onto the baking tray from the narrow side at a distance of 2 cm. Spray red fruit jelly dough between the strips. From the long side, draw lines through the dough with a wooden stick at 2 cm intervals, alternating from left to right. Bake the dough in a preheated oven (electric: 175 °C/ gas: level 2) for 25-30 minutes. Let them cool down. Cut out approx. 20 circles with a round cookie cutter (approx. 7 cm Ø)