In a blender, combine ice cream, 1 cup milk, and mint extract. Pulse until smooth and creamy. Add milk ¼ cup at a time until desired consistency is reached. (I like mine a little thicker so I”™d stick with 1-1/2 cups but if you want it thinner, like a drink- just add more milk!) Drizzle chocolate syrup in desired serving glasses so that it is swirled around the sides (see pictures). Pour shake into glasses. Top with whipped cream and sprinkles if desired. Enjoy!