Separate eggs. Beat egg whites and 2 tablespoons of cold water until stiff. Add 75 g sugar, 1 packet of vanillin sugar, salt and ground saffron. Fold in the egg yolk. Mix flour, starch and baking powder, sieve onto the egg mixture and fold in carefully.
Line the bottom of a springform pan (24 cm Ø) with baking paper. Fill in the dough, smooth it down and bake in the preheated oven (electric: 175°C/ gas: level 2) for about 20 minutes. Remove from the tin and let it cool down on a cake rack.
Meanwhile wash the plums, cut them in half, stone them and cut them into small pieces, except for 2 pieces. Sprinkle with 3 tablespoons of lemon juice. Soak the gelatine in cold water. Stir the quark, remaining lemon juice, sugar and vanillin sugar until smooth.
Squeeze the gelatine, dissolve and stir into the quark and keep cool. Cut the sponge cake horizontally once. Spread the bottom layer with plum jam and place a cake ring or the edge of a springform pan around it.
Whip 200 g cream until stiff and, as soon as the quark begins to set, fold in the plum cubes. Spread the quark cream on the lower cake base. Cover with the second cake base, press down slightly and refrigerate for about 20 minutes.
Whip the rest of the cream until stiff and spread the cake with half of it. Fill the other half into a piping bag with star spout and squirt tuffs onto the cake. Cut the remaining plums into slices and decorate the cake with them.