In a medium bowl, stir together the flour, sugar, baking powder, and salt. Set aside.Advertisement
Place the butter and chocolate chips into a microwave-safe bowl. Cook on High power for 1 minute, then stir. Continue to cook for 15 seconds at a time, stirring each time until chocolate is melted and smooth. Set aside to cool slightly.
When the chocolate mixture is fairly cool, stir in the milk, egg whites, and vanilla. Pour this into the dry ingredients, and mix just until blended.
Preheat the waffle iron, and coat with cooking spray. Spoon waffle batter onto the hot iron in desired amounts. Close, and cook until the iron stops steaming, and waffles are easy to remove. Repeat with remaining batter.