Preheat the oven to 175°C and line a baking tray with baking parchment.
Sift the plain flour in a mixing bowl.
Next, break the butter into small chunks and add them to the sifted flour.
Rub the butter into the flour, using your fingertips and thumbs only, until you have a fine breadcrumb texture with no large chunks of butter left in the bowl.
Next add the sugar and chocolate chips, and mix everything together.
Press the mix together in the bowl. If it sticks together but is still crumbly and easy to break, you’re ready to shape. If you basically still have breadcrumbs, add the milk. The additional moisture should be enough to bring the dough together if you knead it 2-3 times. Don’t over-knead or make the mix too wet though or the shortbread will be hard and chewy.