Add all dry ingredients to a bowl and stir to combine
Heat butter in a small saucepan to melt, and add this to the milk
Start to heat waffle iron
Add spinach, milk and butter mixture to dry ingredients, and whisk. Do not whisk until smooth. Some small lumps are expected, and if you whisk until smooth you will have overworked mixture.
Add the lemon juice and whisk for a few seconds more to combine.
Grease waffle iron with melted mixture and cook waffles, each using one ladle of mixture. Wait for steam to die down before opening waffle iron. Serve immediately, or store to freeze and reheat.