In a large mixing bowl, add your flour, baking soda and salt and mix well. Set aside.
In a separate mixing bowl, add your softened butter, sugar, and brown sugar. Beat together until smooth and creamy. Add in your vanilla extract and mix well.
Slowly add your flour mixture, and mix until just combined. Fold through your chocolate chips. If the dough is a little crumbly, add the milk, one tablespoon at a time. Cover the cookie dough and refrigerate for at least 2 hours.
Remove the cookie dough from the refrigerator. Preheat the oven to 180C/350F. Once warm, form 6 balls of cookie dough and place on a cookie sheet. Bake the cookies for 12-15 minutes, or until the edges go slightly brown. Remove from the oven and let cool for 10 minutes on the sheet, before transferring to a wire rack until cool.
* Only add the milk as needed. If your dough is firm and formable, do not add any. Levain Bakery Cookies can keep at room temperature, covered, for up to 14 days. They can also be stored in the refrigerator and freezer.