In a large bowl, whisk together the flour, baking powder, cinnamon, salt, granulated sugar, and brown sugar until well combined.
In another bowl, mix the milk, melted butter, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. Gently fold in the diced apples and nuts if using.
Preheat your waffle iron according to the manufacturer's instructions. Lightly grease it with cooking spray or oil.
Pour enough batter into the waffle iron to cover the surface, close the lid, and cook until golden brown (about 3-5 minutes). Repeat with the remaining batter.
While the waffles are cooking, prepare the glaze by whisking together the powdered sugar, milk, and vanilla extract in a small bowl until smooth.
Once the waffles are done, remove them from the waffle iron and let them cool slightly. Dip the tops into the glaze and let the excess drip off.
Serve warm and enjoy your delicious apple fritter waffle donuts!