Preheat oven to fan forced 180°C and line a 23cm square pan with baking paper that comes up over the edges for easy removal.
Place sugar, butter and vanilla into TM bowl and chop 5 sec/speed 6. Cook 15 min/Varoma/speed 2.
Add salt and incorporate 30 seconds on speed 4.
Add eggs, yolk and cocoa to TM bowl and mix 15 sec/speed 5.
Scrape down sides of bowl and add flour and nuts and mix 3 sec/speed 5.
Spread into prepared pan, stud with additional nuts, sprinkle generously with additional salt flakes and bake for 10 minutes.
Remove from oven and bang on bench quite firmly to prevent rise from continuing. Return to oven for a further 10 minutes or until just wobbly in centre.
Allow to cool slightly in tin before cutting into enormous pieces and wolfing down immediately!