Puree the raspberries and pass through a sieve. Cream fat, sugar and salt with the whisk of the hand mixer. Stir in the eggs one by one. Mix flour and baking powder and stir in. Halve the dough.
Stir 3 tbsp. raspberry puree under one half and fill into a greased and flour-spread box form (approx. 11 x 30 cm). Smooth the dough and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see
manufacturer) Bake for 15-20 minutes. Use the rest of the raspberry puree for other purposes.
Remove the cake from the oven, let it cool down for about 10 minutes and turn it over. Let it cool down on a cake rack. Clean, dry, grease and sprinkle with flour. Stir cocoa and milk into the other half of the dough and put it into the tin.
Smooth the dough and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for 15-20 minutes.
Remove the cake from the oven, let it cool down for about 10 minutes, turn it over and let it cool down on a cake rack. Bring jam to the boil in a small pot. Cut both cakes in half lengthwise and coat them all around with jam.
Put the cake strands together like a chessboard. Coat the outside with the remaining jam again.
Knead the fondant until smooth, if necessary heat it up very briefly in the microwave. Roll out the fondant rectangularly (approx. 34 x 42 cm) on a work surface sprinkled with icing sugar. Cover the cake with the fondant and press the edges firmly together.
Cut off excess fondant at the bottom edge of the cake. Chill the cake until serving, then decorate with sugared rose petals.