In a blender, combine milk, spinach, eggs, vanilla, oil, vinegar, and maple syrup. Blend until smooth and spinach is completely pureed. Set aside.
In a medium-sized bowl, add the flour, baking powder, cinnamon, salt, and cocoa powder. Whisk together to combine.
Pour the contents of the blender into the bowl with the dry ingredients. Stir until just combined. Do not over mix or your waffles will be dense.
Stir in the chocolate chips, if using.
Heat your waffle iron on medium-high. Once it’s ready, spray both sides with oil then spoon about ⅓ cup of the waffle batter onto the iron.
Cook until you no longer see steam escaping from the waffle iron and waffles are crisp on the outside, about 4 to 5 minutes.
Carefully remove the waffle from the iron and transfer to a plate or cooling rack. Repeat until all batter is cooked.
Enjoy warm or let cool and store in fridge or freezer for future use!
