Have you ever tried to transform a cake into a bread? Well this is what I've done with this experiment. I took a bunt cake recipe, where the rising agent was baking powder and baking soda and do some adaptations to rise it exclusively with sourdough.
The first, I baked the no sourdough version to see if I like it. As it resulted in a delicious cake, I adapted the recipe so I give up on baking powder and baking soda and introduce only sourdough. The result was absolutely impressive and I know for sure that I'll do this more often in the future.
Before launching myself into such an experiment, I did a bit of research on google to see how others have done it. Unfortunately, most of the recipes I found had sourdough in the title but actually it was not the main rising agent of the cake because they were adding baking powder. In this case, the sourdough mentioning looked faked to me because sourdough was used just like an extra ingredient without having any significant importance in the rise of the cake.
I had some experience with rising sweet bread in the past, see Romanian Sourdough Sweet Bread (Cozonac cu maia) but not with bundt cakes/bread where the dough is more hydrated, being in fact a batter.
My first concern when adapting the recipe was the preservation of the ingredients during the rising time. For a classical bread, a dough made from flour and water can stay at room temperature during 1 day without any problem, but when we are talking about adding ingredients like puree, eggs, things are changing as their perishable property needs to be considered. What I did to avoid this was to let the mixed butter (already put in the pan) in the fridge overnight. This benefitted from a cooling time (reduced unwanted bacteria development) while increasing the flavours. There is another aspect that balance this. The introduction of the sourdough adds a level of acidity in the batter that contributes to a better preservation of the ingredients. That's why, let's say that for this version I was extra cautious because in the case of the Cozonac cu maia the rise was at room temperature with no risk of altering the healthiness of the ingredients.
Taking into account the above considerations, I think that there is no risk if the rise is done at a room temperature over the day without needing to retard the batter in the fridge.
For this recipe I used stiff starter, at 50% hydration. Why? Simply because stiff starter has low acid taste and is more appropriate for sweet breads rather than 100% hydration starter.
I am sure you ask yourself which one was was better? With sourdough or without?
I found the sourdough version more soft, moist and flavoured than the one without sourdough. However the differences in taste I think they were minor, they were more just nuances. As for healthiness, I think there is no doubt which one is better.
There are differences in the methods of doing the 2 versions. The sourdough one takes longer and cannot be done in one shot like the no sourdough version can be. If you are a sourdough geek like me, most probably you'll find worthy to spend more time and make the sourdough version. If you are not, go for the no sourdough version.
Please also note that the temperature of baking is different between the versions and I can tell you that if you increase the temperature of the oven for the one with baking powder you might experienced cracklings. Otherwise, in the aspect they look almost identical. Maybe just the version with sourdough is lighter as colour due to the sourdough addition. I didn't photograph the no sourdough version but they are very similar as aspect.
Bellow are the 2 versions, which one are you tempted to try?