Preheat the oven to 350. Grease a loaf pan or 8 x 8 baking dish with cooking spray and set aside. In a large mixing bowl, combine the dry ingredients and mix well. In a small bowl, whisk the milk, vanilla extract and egg/flax egg. Pour into the dry mixture. Add the melted nut butter (and honey and applesauce for paleo option) and mix very well until a batter is formed. Divide the batter in half. In one half, fold through the blueberries. Pour the blueberry filled batter to evenly cover the baking tray or loaf pan. Top with the other half of the batter. Bake for 25-30 minutes, or until golden brown on top and a toothpick comes on clean. Remove from oven and allow to cool completely before serving or frosting, if desired.