Preheat your oven to 180 degrees celsius. Place 18 paper muffin liners into a 12 x 2-hole muffin trays and set aside until needed..
Place the butter into your Thermomix bowl and cook for 2 minutes, 60 degrees, speed 2 to melt.
Add the cored and quartered apples to your Thermomix bowl and use the 2 second turbo function 2 - 3 times to chop into small pieces.
Add the eggs, milk and vanilla extract and mix for 15 seconds, speed 4.
Add the self raising flour, baking powder, cinnamon, and caster sugar to your Thermomix bowl and mix for 10 seconds on speed 4.
Scrape down the sides of the bowl and mix for a further 5 seconds on speed 4.
Spoon the mixture into the prepared cases (filling 2/3 of the way to the top) and place into the oven to bake for 18 - 20 minutes or until cooked when tested with a skewer.
Allow to cool in the tray for 5 minutes before transferring onto a wire rack to cool completely.