Heat the butter for a few minutes to melt down until smooth
Once melted, keep cooking the butter in the pan for a further few minutes, for the milk solids to start to brown. You are looking for a deeper caramel colour
Make sure to swirl the pan and stir slightly to stop anything from burning
Once browned, pour the brown butter into a new bowl to cool fully
The cookie dough
Add the browned butter to a mixing bowl, with the sugar, and beat together until combined
Add the egg, and vanilla and mix again
Add the flour, cornflour, baking powder, bicarb and salt and combine
Add the chocolate and mix through
Split the cookies into 8-9 balls (about 120g each) and chill for 30 minutes in the freezer or 60 minutes in the fridge
Preheat the oven to 200ºc/180ºc fan and line two large trays with parchment paper
Bake the cookies in the oven for 11-13 minutes
Leave to cool for at least 30 minutes on the tray and enjoy
Notes
These will last 5-7+ days at room temperature, or in the fridge