Cream 125 g butter, 200 g sugar, vanillin sugar, lemon zest and eggs with the whisks of the hand mixer. Add milk and mix. Mix flour, salt, espresso powder and baking powder and stir into the egg-sugar mixture in portions
Grease a square springform pan (24 x 24 cm) and sprinkle with flour. Pour in the dough and bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 45 minutes. If necessary, cover the cake with aluminium foil about 10 minutes before the end of the baking time.
Wash the plums, dab dry, cut in half and remove the stones. Cut the plums into slices. Caramelise 100 g sugar in a pan until golden. Add 25 g butter, plum wedges and lemon juice and bring to the boil (caramel must have dissolved completely). Mix starch and 2 tablespoons of water, pour into the plums and let simmer for about 5 minutes while stirring. Remove the plums from the heat, stir in the cognac and allow to cool
Remove the cake from the oven and spread plums on top. Beat the egg whites until stiff and gradually add 175 g sugar. Fold in grated coconut. Carefully spread the meringue mixture with a tablespoon, leaving an approx. 1 cm wide rim. Bake for another 15 minutes at the same temperature.
Remove the cake from the oven. Remove the cake from the edge with a knife and let it cool in the mould on a cake rack for at least 3 hours