Prepare the Dry Ingredients: In a large bowl, whisk together flour, sugar, baking powder, salt, and cinnamon. Set aside once mixed.

Mix the Wet Ingredients: In another bowl, combine milk, eggs, melted butter, and vanilla extract. Whisk until smooth, then pour into dry ingredients.

Combine Wet and Dry Ingredients: Gently fold the wet mixture into the dry ingredients using a spatula. Stir just until combined, batter should be thick and slightly lumpy.

Add Apples: Fold in the diced apples until evenly distributed. Let the batter rest for about 10 minutes.

Preheat the Waffle Iron: Set the temperature to medium-high and preheat according to manufacturer's instructions.

Grease the Waffle Iron: Lightly grease the preheated waffle iron with vegetable oil or non-stick spray.

Spoon the Batter: Spoon about a cup of batter for each donut shape into the greased waffle iron. Cook for about 4 to 5 minutes or until golden brown.

Cool the Waffles: Place cooked waffles on a wire rack to cool for a few minutes.

Cut Donut Shapes: Use a donut cutter to cut out shapes from cooled waffles. Save scraps for donut holes.

Heat Oil for Frying: Heat vegetable oil to 350°F (175°C) in a deep pot or fryer.

Fry the Donuts: Fry in batches for 2-3 minutes each side until golden brown. Turn gently to avoid splattering.

Drain the Donuts: Remove with a slotted spoon to drain excess oil on paper towels.

Prepare the Glaze: Whisk together powdered sugar, milk, and vanilla extract until smooth and glossy.

Dip the Donuts: Dip each donut into the glaze and let excess drip off before returning to wire rack.