Using a handheld or stand mixer fitted with the paddle attachment, beat the butter until smooth and creamy. Add the icing sugar and beat until light and fluffy.
Add the egg and vanilla, and beat until combined. Add the flour and salt, and beat until combined. Fold in the chocolate chips.
Turn the dough out onto a lightly floured surface and shape into a 12-inch long log (about 2 inches wide), or two 6-inch logs.
Tightly wrap the log in clingfilm and chill in the fridge for at least 4 hours, and up to 5 days. I like to chill mine overnight.
Preheat the oven to 180C/350F/Gas 4, and line a baking tray with parchment paper or a silicone mat. Set aside.
Slice the log into thick slices, and place them onto the prepared baking tray. Bake for 12 - 14 minutes until lightly brown around the edges.
Allow to cool for 5 minutes before transferring them to a wire rack to cool completely.
Notes
Cookies stay fresh covered at room temperature or in the fridge for up to 1 week. They also freeze well for up to 3 months. Thaw overnight in the fridge.Cookie dough logs freeze well for up to 3 months. Thaw overnight in the fridge before slicing and baking.