Sourdough brownies use a sourdough starter to add a little tanginess to every chocolatey bite!
Add sourdough starter and stir by hand until smooth.
Pour brownie batter into prepared pan and bake for 25-28 minutes or until an inserted toothpick is removed with a few crumbs but no wet batter. Do not overbake. (Every oven is different so start checking at 22 minutes just in case!)