Wash, halve and stone the plums and sprinkle with lemon juice and plum water. Mix fat and sugar with the whisk of the hand mixer for about 8 minutes until creamy. Stir in salt and lemon peel. Stir in the eggs one by one. Mix flour, starch and baking powder and stir in. Put half of the dough into a greased springform pan (26 cm Ø) and smooth it down. Spread plums (put 4 halves aside for decoration) on top.
Cover with the remaining dough. Bake the cake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 hour. Mix cinnamon and cane sugar and sprinkle over the cake after 30 minutes. Take out and let cool in the mould. Cut remaining plum halves into slices. Decorate the cake with sugar crystals and plum wedges