For Cinnamon Sugar coating - In a mixing bowl add castor sugar and cinnamon. Keep it aside.
In a small bowl mix all dry ingredients listed under batter.
Whisk in melted butter, egg, vanilla extract, and milk to the dry ingredients. The batter has to be smooth and lump-free.
Cut apple into slices with medium thickness (not too thin or too thick). Using apple corer or a knife remove the center (the core) of apple slices.
In a deep frying pan/sauce pan heat oil to medium heat.
When the oil reaches 365F (185C) in a kitchen thermometer or when you drop a spoonful of batter to the pan and the batter sizzles and rises to the top (refer the video below) , the oil is ready for frying.
Dip one apple slice at a time to the batter, coat well on both sides and slowly drop into the oil by hand or a fork. Within seconds the apple rings would rise and float.
Repeat the above process and drop 1 or 2 more apple slices well coated with batter.
Fry for 1 minute on each side or until it is nice golden in colour.
Use tongs to remove apple fritters, drain excess oil, and keep it in a kitchen towel lined plate.
Before frying, another batch let the oil heat for some time and reach 365F (185C).
While the fritters are still warm, dip one fritter at a time to the cinnamon-sugar mixture prepared in step 1. Coat well on both sides.
Don't miss the detailed Video of making Apple Fritters below.