In a large bowl, whisk together the 2 ¼ cups oat flour or gluten free flour, ½ cup light or dark brown sugar, 2 teaspoons baking powder, 1 teaspoon baking soda, 2 teaspoons ground cinnamon, ½ teaspoon ground ginger, ¼ teaspoon ground nutmeg, and ¼ teaspoon fine sea salt.
In a medium bowl, lightly beat the 3 large eggs, then whisk in the 1 cup pure pumpkin puree, ¼ cup unsalted butter, and 1 ½ cups milk. Stir the wet mixture into the dry ingredients and let the batter stand for 15 minutes.
Heat the waffle iron on the highest setting. Then, when the batter has rested, scoop ¼ cup of batter into the iron, close the lid, and cook until done. Repeat until all the batter has been used up.
Notes
Rest the batter. I always let the batter for waffles and pancakes rest for at least 15 minutes, regardless of whether it's a gluten-free batter or not. This helps the flour to absorb moisture (especially important in gluten-free recipes), which in turn leads to a fluffier waffle. I find that 15-20 minutes is just fine. If your batter is a tad thick, you can stir in a few tablespoons of milk to help it become more pourable.
Rest the batter overnight. You can even let the waffle batter rest overnight in the fridge to deepen the flavor and allow the batter to really hydrate. If you try this, place the batter in an airtight container and store it in the fridge. You may need to loosen it up with a few tablespoons of milk if it's become very thick.
What setting? I like to cook my waffles on the waffle iron's highest setting to make sure they are fully cooked inside and slightly crisp on the outside.
What size? I like to make my waffles using a ⅓ or ½ cup measure, but you can make them as large or small as you like.
How long to cook waffles? Cook the waffles until the light changes to green and there's no more steam coming off the top of the machine. This might mean you need to cook the waffles a bit longer after the light changes. Add milk. Gluten-free flour absorbs more liquid than all-purpose flour. You can add a little more milk, 1 tablespoon at a time, if you find that the batter is too thick to add to the waffle iron.
Make dairy-free. Make waffles dairy-free by substituting non-dairy butter for the butter, your favorite non-dairy milk for the milk, and non-dairy yogurt for the yogurt.
Swap coconut oil. I like to substitute the butter with unrefined or refined coconut oil for a change. The waffles are just as buttery and tender.