1. In a large mixing bowl, beat the softened butter, brown sugar, and granulated sugar together until light and fluffy.
2. Add the milk and vanilla extract, mixing until well combined.
3. Gradually add in the flour and salt, stirring until a smooth dough forms.
4. Fold in the chocolate chips until evenly distributed.
5. Line a baking dish with parchment paper and press the cookie dough evenly into the pan. Smooth out the top.
6. Place the dish in the refrigerator for about 1 hour, or until firm.
7. Melt the chocolate chips with the coconut oil (or butter) in a microwave-safe bowl in 30-second intervals, stirring in between until smooth.