Beat together the butter and sugar using a hand mixer until well combined and creamy. Add the vanilla extract and paste, then the egg and beat in well.

Sift together the flour and baking soda, add to the mixture and stir with a wooden spoon until it just comes together into a dough. Fold in the chocolate pieces, then chill overnight, or for up to 72 hours.

Preheat the oven to 350F (180C). Line two baking trays with parchment paper, and divide the mixture into golf-ball sized rounds (about a tablespoon each), spacing them well apart. Bake for about 15 minutes, until golden.

Sprinkle lightly with sea salt if using, and allow to cool on the tray for a couple of minutes, before moving to a wire rack to cool completely.