Melt the butter in a small saucepan until sizzling. Watch it carefully – the butter will foam, and, when the foam subsides, it will turn from yellow to a hazelnut brown. At this point, remove from the heat, tip into a bowl and leave to cool. Meanwhile, mix the flours, salt, baking powder and bicarb together in a bowl and set aside.

When the butter is cool, tip in the sugars and beat with a wooden spoon to combine. Add the egg, yolks and vanilla and beat together. Scrape the wet mixture into the dry ingredients and stir until it all comes together into a dough. Fold in the chocolate, then chill for at least 3 hrs, or until firm. Will keep chilled for up to 24 hrs.

Heat the oven to 180C/160C fan/gas 4. Line two large baking sheets with baking parchment. Separate the dough into 12 pieces, weighing for accuracy if you like. Roll each piece into a ball using your hands, then put six balls on each sheet, leaving space between them for spreading. Bake for 10 mins, then, one sheet at a time, remove from the oven, sprinkle with some sea salt and slam the sheet hard against your work surface.

Bake for another 3 mins, then repeat the slamming of the sheet. Bake for 3 mins more. This timing will give you soft cookies, but if you prefer them a bit firmer, cook for a few minutes longer. Leave to cool on the sheets for 10 mins before transferring to a wire rack to cool completely.