In the bowl of a stand mixer with the paddle attachment, beat the butter for 2 minutes on medium speed. Add the sugars and beat for a further 2-3 minutes. Scrape down the sides of the bowl to ensure all of the butter is fully incorporated.
Add the eggs one at a time on low speed until just incorporated.
Add the dry ingredients and beat until fully incorporated.
On low speed add the chocolate chips and walnuts to combine.
Weigh each cookie dough ball to 150g. Chill in fridge for at least 3 hours before baking.
When ready to bake, preheat the oven to 180°C and line a baking tray with baking paper. Place cookie dough balls onto the tray, at least 2cm apart, top with sea salt flakes if using and bake for 16-18 minutes until golden on top.
Allow to cool for 10-15 minutes before enjoying (the cookies need this extra time to continue cooking at room temperature).
Notes
I didn't have chocolate chips, but I did use 100g dark chocolate and 200g white chocolate roughly chopped and it turned out beautifully too.