For 20-25 minutes. (If the mini chocolate chips are already mixed into the batter you will have to add 5 minutes to the cooking time.) Check the center with a wooden toothpick for doneness, and if the center has not cooked, bake for an additional 5 minutes. (The mini chips will be melted throughout the brownies so your toothpick may emerge covered in chocolate. Using another toothpick, try a different spot.) When the toothpick emerges with only a crumb or two adhering to the surface, the brownies are done.