Method

• 1.
  Line a rimmed baking tray (two, if you’ve got ’em) with baking paper.
• 2.
  Using a stand mixer fitted with the paddle attachment, beat the butter, both sugars and vanilla on medium-high till super light and fluffy, 3-5 minutes. Using a spatula, scrape down the sides of the bowl and, with the mixer on low, slowly add the flour, followed by the chocolate chunks, and beat just to blend.

• 3.
  Divide the dough in half, placing each half on a large piece of plastic wrap. Fold the plastic over so that it covers the dough to protect your hands from getting all sticky. Using your hands (just like you’re playing with clay), form the dough into a log shape; rolling it on the counter will help you smooth it out, but don’t worry about getting it totally perfect. You can also do this using baking paper, if you prefer, but I find using plastic wrap easier when it comes to shaping the log. Each half should form two logs 5-7cm in diameter. Chill until totally firm, about 2 hours.
• 4.
  Preheat the oven to 175°C.
• 5.
  Brush the outside of the logs with the beaten egg and roll them in the demerara sugar (this is for those really delicious crispy edges).
• 6.
  Slice each log into 1.5cm-thick rounds, place them on the prepared baking tray(s) about 2cm apart (they won’t spread much) and sprinkle with flaky salt.
• 7.
  Bake until the edges are just beginning to brown, 12-15 minutes. Let cool slightly before eating them all.