Herman the German Friendship Cake

Hello my name is Herman.
I am a sourdough cake.
I am supposed to sit on your benchtop for 10 days without a lid on me.
You cannot put me in the fridge or I will die.
If I stop bubbling I am dead.

Day 1 : Put me in a large mixing bowl and cover loosely with a tea towel.
Day 2 : Stir well.
Day 3 : Stir well.
Day 4 : Herman is hungry. Add 1 cup of sifted plain flour, 1 cup of sugar and 1 cup of milk. Stir well.
Day 5 : Stir well.
Day 6 : Stir well.
Day 7 : Stir well.
Day 8 : Stir well.
Day 9 : Add 1 cup of sifted plain flour, 1 cup of sugar and 1 cup of milk. Stir well. Divide into 4 equal portions and give 2 portions to friends. Keep 1 portion for later and use 1 portion to cook me tomorrow
Day 10 : I am ready for the final stage.

Add the following to me: 1 cup of sugar, 2 cups of sifted plain flour, 2 heaped tsp baking powder, 1/2 tsp salt, 2/3 cup of cooking oil, 2 eggs, 1 tsp of vanilla esssence, 2 heaped tsp of cinnamon. Mix well then mix in 2 chopped cooking apples and 1 to 2 cups of sultanas.  Pour into a prepared cake pan. Sprinkle 1/2 cup melted butter and 1/4 cup brown sugar on top of the cake, then bake for 45 minutes at 170 to 180 degrees Celsius.  Test the middle with a skewer.  You may need to cover with aluminium foil and bake for a further 20 minutes until set.  When baked I can be frozen.