Ingredients:
Scald milk (do not boil), stir in sugar, salt, butter. Cool to luke warm. Measure water into a large, warm bowl. Sprinkle in yeast and stir until dissolved. Stir in milk mixture (after it has cooled to lukewarm), egg, and half the flour. Beat with hand mixer until very smooth, keep adding flour as long as mixer can handle it. Add remaining flour until somewhat stiff, kneading by hand. Done when it becomes one cohesive batter that is very smooth, sticks together, but doesn't stick to your hands. Cover it loosely with aluminum foil, and refrigerate for at least two hours (or leave it outside in a warm place if you want to use immediately). Dough may be kept in refrigerator for up to three days.
This makes a lot - if you want to make half, still use the full packet of yeast and one egg, halve the other ingredients. You might need more than half of the flour.
One half (or less) portion makes one cookie sheet of cake. Gudrun put the plums on immediately. Helga puts plums on with some mixture of cinnamon/sugar, and then lets it rise in the oven at the lowest oven before baking it. Bake at ~325-350 degrees for ~45 minutes.
For the topping, add cinnamon to taste, and a small portion (tip-of-knife) of baking powder. Crumble it together, crumble over the cake before baking.
The plums can be substituted with apples or other fruits (e.g. berries, ...), or a butter/milk/sugar topping (zuckerkuchen, similar to bienenstich without the filling).