The night before, brown your butter in a small saucepan. It should be very golden brown in colour. Don’t be conservative – the dark brown gives the cookies tonnes of flavour and weight is important here. Weigh it once browned – it should weigh 130g or close to that. Any deviation of above a gram or two could have an unwanted effect on your cookie.
Once browned and weighed, add the butter to the sugars in a small heatproof bowl. Stir to combine, and set aside to cool. Be careful – the bowl will get quite hot.
Weigh out your flours and add the salt, baking powder and baking soda. Use a whisk to thoroughly combine.
Once the butter mixture has cooled a little, add the milk and vanilla bean paste, stirring to combine. Finally, add the egg. Adding the egg after the milk will help ensure it doesn’t cook in the residual heat of the butter.
Mix the dry ingredients into the wet. I like to start in the middle, and gradually mix in the edges of the bowl until all the flour is completely combined. Not a bit of flour should be left on the side of the bowl.
The cookie dough should look wet, almost like a thick caramel in colour in texture. Cover it and place it in the fridge overnight.