Whisk together the flour, cocoa, baking powder and baking soda in a large bowl.  In a smaller bowl cream the butter, sugar and eggs together with a mixer.  Add vanilla extract, milk and sourdough starter and continue mixing.  Pour into flour mixture and continue mixing until all ingredients are wet.

Stir in 1/2 the chocolate chips and pour batter into a sprayed 9 x 5 baking pan.  Sprinkle remaining half of the chocolate chips on top of batter.  Bake in preheated 350 degree oven for 45 to 50 minutes until center tests done. Let cool for 10 minutes before removing from pan