For the crust: Mix the fresh yeast with 2 tablespoons of the sugar and reserve. Mix into the hot milk the remaining sugar, salt, oil, butter, vanilla sugar and half of the cake flour in a bowl of a kitchen aid mixture or food processor, mix at low speed for 1 minute. Add the egg. Add the yeast/sugar mixture. Add the remaining cake flour and mix well at low speed until all ingredients are incorporated. Let rise at a warm place until dough doubles. With a rolling pin, roll out the dough to fit a 12 by 17-inch cake pan, which is lightly buttered and dusted with flour.
For the topping: Preheat oven to 360 degrees. Sprinkle hazelnut flour over the dough. Cut the plums open but not in half, remove the pit and cut a small insert into the top. Layer standing on top of the dough. Mix sugar, cinnamon, and bread crumbs and sprinkle over the plums. Top with almonds and butter. Bake on the second shelf from the bottom for 45 minutes to 1 hour at 360 degrees in a regular oven or for 45 minutes at 300 degrees in a convection oven. Let cool, serve by itself, or with whipped cream, ice cream, or cinnamon creme fraiche.