Make a batter from (the first 8 ingredients) flour, pudding powder, margarine, sugar, egg, salt, baking powder and flavor. Put the dough in a springform pan, except for a third. Spread the remaining dough on the edge of the mold and pull up.
Wash the plums well, stone them and cut them in half. Spread the halved plums on the cake batter. Now knead the remaining 6 ingredients to crumble and distribute on the plums.
Bake in a preheated oven at 180 ° C for about 35-45 minutes.