In a large mixing bowl, whisk together the flour, sugar, baking powder, salt, and cinnamon (if using) until well combined.
In a separate bowl, beat the eggs, then add the milk, vegetable oil (or melted butter), and vanilla extract. Mix until smooth.
Pour the wet ingredients into the dry ingredients. Gently fold the mixture together with a spatula until just combined; be careful not to overmix. The batter should be slightly lumpy.
Preheat your waffle iron according to the manufacturer's instructions. Once heated, lightly grease the iron with non-stick spray or brush with oil.
Pour an appropriate amount of batter onto the preheated waffle iron (about 1/2 to 3/4 cup, depending on the size of your waffle iron). Close the lid and cook according to the manufacturer's recommendations, usually about 4-5 minutes, or until the waffles are golden brown and crispy.
Carefully remove the waffles and place them on a cooling rack while you continue to cook the remaining batter. This prevents them from getting soggy.
Serve the waffles warm with your favorite toppings such as fresh berries, maple syrup, whipped cream, or a dusting of powdered sugar.