Cook fudge by heating cream on medium heat until steaming but not yet boiling. Remove from heat and stir in chocolate chips and mint extract. Set aside to cool slightly.
Pulverize two thin mint cookies in a blender until powder. Add in sugar and pour onto a small plate. Fill a clean bowl with water, then dip the rim of your glass into the water. Shake off excess liquid, then dip the rim into the powdered cookie mixture. Set aside.
Combine all shake ingredients in a blender. Begin with 3 tablespoons of whole milk, and add more as needed, one tablespoon at a time.
Drizzle fudge sauce onto the sides of the glass, then pour in shake. Top with a few sprigs of fresh mint and a thin mint cookie.