Preheat oven to 180°C and line oven trays with baking paper.
Place rolled oats into the Thermomix bowl and chop 3 sec/speed 6. Set aside.
Place nuts into the Thermomix bowl and chop 3 sec/speed 5. Set aside.
Place chocolate into the Thermomix bowl and chop 4 sec/speed 5. Add to the nuts, reserving some for the top of the cookies.
Place both sugars into the Thermomix bowl and mill 8 sec/speed 9. Add butter and vanilla and whip 30 sec/speed 4.
Add eggs, sourdough starter (discard), baking soda, baking powder, salt and oats. Blend 20 sec/Reverse/speed 6.
Transfer mixture into a large bowl and add the nuts and chocolate. Stir to combine.
With wet hands, roll golf ball sized balls of cookie dough and place onto prepared trays. They will flatten a lot while baking, so leave plenty of space between them. Top with extra chocolate and a decent sprinkle of pink salt flakes.
Bake for 10-12 minutes. Cool on wire racks.
These can be frozen and thaw very quickly at room temperature.