Preheat oven to 350℉ / 180℃
Grease and line a 9 x 9 inch baking pan.
Melt the butter and the chocolate chips in a saucepan.
Once melted, remove from heat and add vanilla and cocoa powder.
Stir until smooth and allow to cool slightly.
Meanwhile, in a large mixing bowl, beat together the eggs and the sugars for around 7-10 minutes.
Add the sourdough starter and the chocolate mixture and beat together on low until combined.
Add the flour and fold through with a spatula until just combined.
Pour the mixture into the prepared baking pan.
Bake for 30-35 minutes.
Allow to cool in the pan before cutting into brownie sized pieces.
Enjoy!
