this is essentially a sourdough starter.
I used to follow the "bag on the counter" directions precisely. Then I got tired of it. I just keep it in the refrig in a container, and take out and refresh whenever I want to bake a cake. Actually, if you have a regular sourdough starter, you can use that for the cake. You don't have to maintain 2 different starters.
I made a lot of different flavors.
Applesauce cake: replace half of milk and oil with an equal amount of applesauce. add walnuts, raisins, cinnamon, nutmeg, and a handful of diced apples. Use butterscotch or vanilla pudding mix.
Pumpkin: same as above, but use canned pumpkin vs applesauce.
Lemon poppy seed: lemon pudding, 2 Tbsp poppy seeds, no cinnamon. Lemon extract.
Blueberry white chocolate: add blueberries, white choc chips, and white choc instant pudding.
Banana: replace half of milk and oil with mashed banana or banana babyfood. Add walnuts and choc chips. Use banana pudding.
You can see, the possibilities are endless.
My family calls this "Sunday Cake" because I bake it on Sunday after church. It usually does not make it to Monday, though.