Preheat oven to 400 degrees.
Mix dry ingredients then add milk, oil, and sourdough starter. Stir until combined but without overmixing.
Grease 9 inch circle cake or square brownie pan and pour batter inside.
Bake for 25-30 minutes until the edges and top start to turn slightly brown.
Let cool for 5-10 minutes then turn out onto a plate and enjoy.