Preheat oven to 180 degrees celsius (fan-forced).
Place 12 muffin liners into a 12-hole muffin tray and set aside.
Sift the self raising flour, baking powder and ground cinnamon into a large bowl.
Add the caster sugar and stir to combine. Create a well in the centre of the dry ingredients.
Grate 2 apples into the well.
Whisk the eggs, buttermilk and vegetable oil in a bowl and pour on top of the apple.
Fold together gently (don't worry if there are still a few lumps - be careful not to over-mix or your muffins will be dense).
Spoon the mixture into the prepared cases (filling ⅔ of the way to the top). Sprinkle with the rolled oats and raw sugar.
Cook for 20-25 minutes or until a skewer inserted into the middle comes out clean.
Allow to cool in the tray for 5 minutes before transferring onto a wire rack to cool completely.