6.
While cookies are cooling, prepare frosting. In medium, microwave-safe bowl, add chocolate. Microwave on high for 30 seconds and then stir, repeat as necessary until chocolate is completely melted and smooth. Stir in melted butter and milk until mixture is smooth. Add powdered sugar and stir to incorporate, adding additional milk, if needed, to improve spreading consistency. Frost cooled cookies. Let frosting set before storing. Store in an airtight container placing waxed paper or parchment paper between cookie layers.