Prepare the Batter. In a large mixing bowl, combine the mashed potatoes, flour, eggs, cheddar cheese, baking powder, salt, pepper, and garlic powder. Stir everything together until well combined. If the mixture feels too dry, add a splash of milk to reach a scoopable consistency.
Preheat the Waffle Iron. Heat your waffle iron and lightly grease it with butter or oil. This ensures the waffles crisp up perfectly without sticking.
Cook the Waffles. Scoop about ½ cup of the potato mixture onto the waffle iron. Close the lid and cook for about 5-7 minutes, or until the waffles are golden brown and crispy.