For the dough, whisk 300 g butter and sugar with the whisks of the mixer for about 5 minutes until frothy. First gradually stir in eggs, then buttermilk. Mix baking powder, 220 g flour and starch, stir in briefly.
Quarter the dough and divide it into four bowls. Colour three doughs with the food colouring into different shades of pink - from soft to light pink to pink.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). Grease two springform pans (approx. 18 cm Ø each) and dust with flour. Put 1 portion of dough into each springform pan and smooth it down.
Place both forms on a baking tray. Bake in the oven for 25-30 minutes.
Let the cake bases cool down a little in the moulds, then remove them. Let the cake bases cool completely. Clean the springform pans, grease them again, dust them with flour, fill in the two remaining doughs, smooth them down and bake in the oven as described in point 2.
Allow to cool, release from the moulds and also allow to cool.
Slightly straighten all soils on the surface if necessary. For the filling spread the fruit spread on the three coloured bases. Place the bases on top of each other from bright pink to light, finish with the uncoloured base.
Cover the cake with cling film, refrigerate for about 4 hours.
For the Frosting, whisk butter and icing sugar with the whisks of the mixer for about 6 minutes until foamy. Finally, fold in yoghurt by the spoonful. Spread a thin layer of cream all around the cake, fill the rest of the cream into a piping bag with a rose nozzle.
Decorate the top and sides of the cake with a wave pattern. Chill for 1-2 hours. Keeps refrigerated for 3-4 days.