In a medium bowl, beat together the butter, powdered sugar, and vanilla extract until smooth. Add in the flour and salt and beat until combined. You'll have a crumbly mixture at this point. 

Stir in the chopped chocolate chunks, distributing evenly. Then, beat in the milk until combined- you should have a smooth, creamy dough. Using plastic wrap, form the dough into a flattened disc that is about 1/2 inch thick. Wrap tightly in plastic and place in the freezer for 15-20 minutes. 

Preheat your oven to 325 degrees, and line a small baking pan with parchment paper. Remove the cookie dough from the freezer and cut into 4 large pie pieces. Place the pieces on the baking sheet with a little room between each cookie. Poke a few holes in each cookie with a fork. 

Bake for 20-25 minutes, or until the cookies look dry and just barely golden brown around the bottom edges. Cool completely before enjoying!