Grease a springform pan (26 cm Ø) and sprinkle with breadcrumbs. Cream fat, 125 g sugar, 1 vanilla sugar and salt. Stir in the eggs one by one. Mix flour, starch and baking powder, stir in briefly with milk. Spread into the mould. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/gas: level 2) for about 20 minutes. Let cool down for about 10 minutes
Mix icing sugar and 4 tablespoons lemon juice. Prick the cake base several times with a wooden skewer, sprinkle with the sugared juice, then let it cool completely
Mix jelly powder and 1/4 l cold water in a small pot, let it swell for about 5 minutes. Stir in 100 g sugar. Heat while stirring (do not boil!) until everything is dissolved. Let it cool down. Chill for about 50 minutes until the jelly starts to gel
Whip 500 g cream until stiff. Mix cream cheese, 4 tablespoons juice, 50 g sugar and 1 vanillin sugar. Stir in the jelly bit by bit. Fold in the cream. Place a cake ring (approx. 8 cm high) around the cake base. Spread the cream on top. Chill overnight
Whip 150 g cream until stiff, pouring in 1 vanillin sugar. For the butterfly: Cut the cake in half vertically, put it together on a large plate with the curves. Decorate with cream, citrus slices etc.