I ran the original German recipe through Google Translate for you, works pretty decent, l only had to change a few minor things lost in translation, and it saved me translating myself.
Here it is:
For the base:
80 g erythritol* ground into powder
50 g ground almonds*
20 g coconut flour*
60 g cold butter, cut into pieces
3 eggs
vanilla extract to taste*
For the crumble:
50 g ground almonds*
10 g coconut flour*
30 g cold butter, cut into pieces
25 g erythritol* ground into powder
Vanilla extract* to taste
And
500 g plums, pitted and halved
Preheat the oven to 180 degrees top and bottom heat.
Mix all the ingredients for the base into a dough and then spread it into a springform pan (approx. 24 cm) lined with baking paper.
Scatter the plums in a circle over the dough.
For the crumbles, it is best to first mash or mix all the ingredients with a fork and then “rework” them briefly by hand. Don't knead for too long here, otherwise the crumbles will become too sticky.
Spread the crumble evenly over the plums and bake the cake in the preheated oven for 35 to 40 minutes. After about 20 minutes, it should be covered with aluminum foil so that the crumbles don't turn too brown.
Allow the plum cake to cool in the pan for at least 30 minutes before slicing.