Place 1 paper cups in each of the recesses of a muffin baking tray (12 recesses). Wash, halve and stone the plums. Cut the plum halves into wedges.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer). For the dough, whisk butter, sugar, vanilla sugar and 1 pinch of salt until creamy. Stir in the eggs one after the other.
Mix flour, starch and baking powder, stir in briefly.
Spread the plums into the moulds. Pour the dough over them. Bake in a hot oven for about 25 minutes. Remove the cakes and let them cool down.
For the icing, rinse lemon hot, dab dry and finely grate the peel. Squeeze the lemon. Mix icing sugar and 3 tablespoons lemon juice. Spread the icing on the cake. Sprinkle with lemon peel and let dry.