Preheat oven to 190 degrees celsius (fan-forced). Line 3 flat baking trays with baking paper and set aside.
Place the butter into the Thermomix bowl. Melt for 3 minutes, Speed 3, 80 degrees. Allow to cool slightly.
Add the egg, vanilla extract, plain flour, bi-carb soda, baking powder, salt, brown sugar and caster sugar. Mix on Speed 5, 5 seconds. Scrape down the sides of the bowl and repeat for a further 5 seconds.
Add the rolled oats, dried cranberries and white chocolate chips and mix on Reverse, Speed 3, 10 seconds (or until combined).
Roll tablespoons of the mixture into balls and place onto the prepared baking trays. Bake in the oven for 12-15 minutes or until lightly golden.
Allow to cool on the baking trays for 5 minutes before transferring to a wire rack to cool completely.
Store in an airtight container for up to 7 days (or freeze for up to 2 months).