In a large bowl, whisky together the sugars, salt and butter until a paste has formed with no lumps.

Whisk in the egg and vanilla, beating until light ribbons fall off the whisk.

Sift in the flour and bicarb, then fold the mixture very gently with a spatula. Be careful not to over mix or you could end up with a more cakey textured cookie.

Fold in the chocolate chunks evenly, then chill overnight. Leaving it overnight in the fridge develops a more toffee-like flavour!

When you’re ready to bake, pre heat the oven to 180 degrees fan and line a baking tray with parchment paper. You don’t want to overload the tray as the cookies will spread, so you may have to bake in batches.

Use an ice-cream scoop to shape the dough into balls and place onto the prepared baking tray (you’ll probably fit 5 onto the one tray).

Bake for around 10 minutes, or until barely browning. Leave to cool on the baking tray for around 5 minutes before transferring onto a cooling rack. Leave to cool completely before eating as they will eventually stiffen up!