Cream butter, brown sugar and white sugar using a whisk or a hand blender. If using a stand mixer, use the paddle attachment. Cream till it becomes light and fluffy, about 3 minutes. Add milk, coffee decoction and vanilla extract and whisk till it gets incorporated.
In a separate bowl, sieve together the flour, baking soda and salt and add this to the butter mixture and beat it until it gets incorporated. Add the chocolate chips and fold.
Make 1 inch size balls and chill the dough for 30 minutes. If the dough is soft, refrigerate for 30 minutes before scooping.
While the dough is chilling, preheat oven to 170C
Place balls of cookie dough on a cookie sheet lined with parchment paper a few inches apart as they will spread while baking. Bake for 12-15 minutes or until the edges become golden brown.
Allow the cookies to cool for 5 minutes before transferring them to a wire rack. Cool for 15 minutes before serving.
Use butter at room temperature if using a hand blender or stand mixer. If doing this by hand, use melted butter.
Instead of coffee decoction, you can also mix ½ teaspoon instant coffee powder in 2 tablespoon warm milk and use it