In a bowl, combine dry ingredients: flour, baking powder, cinnamon powder and salt. Stir and set aside.
Into another bowl, combine pumpkin purée, maple syrup, eggs and melted butter. Whisk for a few seconds until combined. Then add milk + vinegar mixture and stir again.
Pour the wet ingredients over the dry ones and use a whisk to incorporate. Remember: do not overmix.
Grease your waffle iron then pour a few tablespoons of the pumpkin mixture. Close and cook until golden brown and crisp.