Preheat the oven to 350°F then lightly grease a loaf (or muffin) pan.Combine milk and apple cider vinegar in a measuring cup and set aside for a few minutes.In a blender, combine all ingredients in the order listed (except chocolate chips). Make sure to put the wet ingredients first otherwise the batter will become too thick for your blender. Blender for about 10 seconds, until smooth. Pour the batter out into the loaf pan and shake until evenly distributed. You may need a spatula to help scrape the batter out of the blender.Bake in the oven for about 45 minutes, until a knife comes out clean when stuck into the center. Allow to cool for at least 30 minutes. Serve with melted peanut butter (optional), and enjoy!