Preheat oven to 350 degrees. Grease an 8x8 baking dish.
Whisk all purpose flour, whole wheat flour, baking soda, and cocoa powder in a bowl.
Mix sugar, eggs, vanilla, and yogurt until combined
Combine dry ingredients into wet ingredients until well mixed. Stir in chocolate chips
Pour batter into greased pan and bake for 35 minutes or until a toothpick inserted has minimal batter on it.