You can use cocoa sourdough starter to bake brownies. This is done by adding chocolate powder instead of flour when adding the water and flour at the last feeding of the starter.
For baking, use freshly ground flour made from green, cold-hulled buckwheat. The bread is light, crumb-free, keeps fresh longer and has a fluffy crumb which is difficult to achieve with gluten-free flours.
Carob is known to have been the first medicine for the poor for stomach cramps. Scientific studies, including one by the University of Zagreb (Link to: 10.17113/ftb.58.04.20.6892), confirm that the quality of bread is much improved by using carob starter.
If we want to have a good active sourdough starter, we need to love and nurture it, then it will give back a lot more than we give. This way we can have the most amazing gluten-free sourdough starter or so called homemade yeast and bake the most delicious fermented gluten-free bread you've ever tasted.
I usually use buckwheat flour to make gluten-free yeast, but occasionally I also use millet or rice flour, chocolate or carob flour. The quickest way to start sourdough starter is with brown rice flour or teff flour. I keep the starter in the fridge and it is the basis for making the active leaven or natural yeast that I use when baking fermented bread.