Preheat a fan forced oven to 155C / 310F (175C / 350F for no fan). Line two baking trays with baking paper, set aside.
To brown the butter - Add the butter to a small saucepan and on a low heat (the lowest on your stove) begin melting the butter. It will begin to bubble and then start turning a light golden color. As soon as it begins to color, begin gently stirring. Once the entire mixture is a golden color (not dark) take it off the heat and allow to cool completely.
Mix dry ingredients - While the browned butter is cooling, add the flour, bicarb soda, baking powder and salt to a small bowl and mix to combine. Set aside.
Mix butter, sugar and eggs - Add the brown butter, brown sugar, caster sugar and vanilla extract to a large mixing bowl and stir using a spatula until combined. Then add the egg and egg yolk and stir until combined.
Finish the cookie dough - Lastly, add the dry ingredients and 200g of dark chocolate chips all at once and mix until a soft dough forms. Mix until evenly mixed through and a dough forms. Use a large ice-cream scoop (just over 2 tbsp in volume) to scoop out 12 cookie balls. You can also weigh the entire cookie mixture and just divide it by 12 to get even sized cookies. Mine came out to about 68g each.
To coat cookies - Coat the cookies in the remaining chocolate chips by rolling them around in the chocolate to help them stick.
Chill time - Place on a baking tray lined with baking paper and chill in the fridge for one hour, or up to 2 days for amazing flavor results! Chill time does two things: 1/ It helps you get thicker cookies and 3/ A cookie with better developed flavors.
To bake - Add 6 cookie balls to a half sheet baking tray lined with baking paper. Bake the cookies in the middle rack of your oven for 10 minutes or until the edges have turned a golden color and the center is still gooey. Once they come out of the oven use a round cookie cutter slightly larger than your cookies to shuffle around the soft cookies and make them round. Then sprinkle with sea salt flakes. Bake the remaining cookies. Allow to cool on the baking trays completely before serving.