Preheat oven to 190 degrees celsius (fan-forced). Line a 12-hole muffin tray with muffin cases and set aside.
Place the chopped apples into the Thermomix bowl. Grate on Speed 8, 10 seconds. Scrape down the sides of the bowl.
Add the remaining muffin ingredients (not the crumble ingredients) into the Thermomix bowl and mix on Speed 5, 5 seconds. Scrape down the sides of the bowl and repeat for a further 5 seconds.
Divide the mixture between the prepared muffin holes (filling to 2/3 full).
To make the topping, place the crumble ingredients into a clean Thermomix bowl and press Turbo a few times until you have achieved a consistent crumble mixture (and all of the dry ingredients have been completely combined with the butter.
Bake for 20 minutes or until golden on top and cooked through.
Leave in the muffin tin for 5 minutes before transferring to a wire rack to cool completely.