Mix the dry ingredients. In a large bowl, whisk together the flour, sugar, baking powder, and salt.
Add the wet ingredients. Add the milk and eggs. Stir just until combined and no dry flour remains. Avoid overmixing.
Fold in the apples. Wash, peel, and core the apples, then chop into small pieces. Fold them into the batter until evenly distributed.
Heat the oil. Pour the oil into a deep, heavy-bottomed pot or deep skillet, leaving plenty of room for bubbling. Heat to 350°F (175°C), checking with a frying thermometer.
Fry in batches. Carefully lower small scoops of batter into the hot oil. Avoid crowding the pan. Fry for approximately 2–3 minutes per side, until golden brown and cooked through. Cooking time will vary with size. Cut open a fritter from the first batch to check for any wet batter in the center.
Drain. Remove the fritters with a slotted spoon and place on a paper towel-lined plate to drain briefly. Let the oil return to temperature before frying the next batch.
Coat and serve. Place the cinnamon sugar in a shallow bowl. Roll each batch of fritters in the mixture while still warm, turning to coat all sides. Serve warm.
