I remember my mum making one of these years ago (there may even have been more than one) and have been meaning to try one myself for years. For the March meeting of the Bury St Edmunds Clandestine Cake Club I decided on an International theme so a German Friendship Cake fitted the bill perfectly.
A quick search on google provided me with a link to a website that has all you need to know about German Friendship Cakes, including the recipe for both the starter and the actual cake. Some advance preparation was required as the starter mix needs 10 days to mature before it can be divided up and made into a cake. Other than that it's a very straightforward process of mixing, stirring and adding more ingredients every few days.
Luckily I had success with my starter, which bubbled and grew just as it was supposed to, filling the kitchen with a distinctive, yeasty smell. Once the starter is ready you add yet more flour, sugar etc plus chopped apples and raisins and then it's ready for the oven.
The final cake was really lovely. Moist and fruity with a hint of sourdough in the background.