Line a baking sheet with kitchen paper and set aside.
Start by making the cinnamon sugar: in a shallow bowl, mix together the cinnamon and caster sugar. Set aside.
For the apple fritters: add the flour, caster sugar, milk and egg into a large mixing bowl and whisk until you have a smooth batter.
Peel and grate the apple using a box grater. Add to the batter with the apple sauce and mix until combined.
Next, pour the vegetable oil into a medium saucepan - it should come at least ½ but not more than ¾ up the side of the pan. Place over a medium heat - it is hot enough when a small piece of apple sizzles after being dropped in. You can also use a deep-fat fryer and heat the oil to 175C.
Once the oil is at the correct temperature, drop in a spoonful of the batter. It should puff up a little. Cook for 2-3 minutes, or until golden underneath, before carefully flipping over and continuing to fry for around 2 more minutes.
When golden all over, remove from the oil using a slotted spoon and set onto the prepared baking sheet. Leave for about a minute to let any excess oil drain off.
Pop the fritter into the shallow bowl of cinnamon sugar and gently toss to coat. Repeat with the remaining batter - as you get more confident you can do up to 3 at a time. Serve straight away.