Preheat oven to 170 degrees celsius (fan-forced). Line two baking trays with baking paper and set aside.
Insert the butterfly into the Thermomix bowl. Add the softened butter, brown sugar and caster sugar. Mix on Speed 4, 2 minutes (scraping down the sides of the bowl occasionally).
Add the peanut butter, egg and vanilla extract and mix again on Speed 4, 1 minute. Remove the butterfly.
Add the plain flour and bi-carb soda. Mix on Speed 4, 10 seconds.
Add the quick oats, M&Ms and chocolate chips and mix on Reverse, Speed 2, 10 seconds (or until combined).
Roll tablespoon-sized balls of the mixture and place onto the prepared trays. Press down slightly. Decorate with extra M&Ms (optional) and then chill for 30 minutes in the fridge.
Bake for 10 minutes or until just starting to turn slightly golden on the very outside (do no overcook - you want them to be soft and chewy).
Allow to cool for 10 minutes on the trays before transferring to a wire rack to cool completely.