Place paper cups in the recesses of a muffin tray (12 recesses). Wash the plums, cut them in half, stone them and cut them into large pieces. Mix with plum puree. Melt butter. Mix flour, almonds and baking powder.
Separate 2 eggs, chill the egg whites. Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer).
Mix butter, 125 g sugar, vanilla sugar and 1 pinch of salt with the whisks of the mixer. Stir in 2 eggs, egg yolks and milk. Stir in the flour mixture. Fold in the plums. Pour in the dough.
Bake in a hot oven for about 15 minutes.
In the meantime, beat the egg whites until stiff, adding 75 g sugar and continuing to beat until the sugar is completely dissolved. Pour the beaten egg whites into a piping bag with a medium star-shaped spout. Remove the muffins from the oven after 15 minutes and immediately spray beaten egg whites as tuffs on top.
Continue baking muffins at the same temperature for about 5 minutes. Remove from the oven and let them cool down on a cake rack.