Preheat oven to 350°F. Prepare two muffin pans with baking cups. Place 1 cookie in bottom of each cup. Reserve remaining cookies for garnish.
In small bowl, whisk together water and cocoa powder.
In large bowl, stir together flour, baking soda, baking powder and salt.
In large bowl, beat sugar, oil, eggs, vanilla and mint extract with electric mixer until well combined. Add cocoa-water mixture; beat until well combined. Add flour mixture alternately with buttermilk, beating well after each addition. Fill baking cups 2/3 full with batter.
Bake 17-19 minutes or until toothpick inserted in center of cupcake comes out clean. Cool cupcakes in pan 5 minutes. Remove to cooling grid and cool completely.
For icing, melt butter in large saucepan. Whisk in cocoa powder and 3/4 of chopped crème de menthe candy until smooth. Transfer to large bowl; cool slightly. With electric mixer, alternately add confectioners? sugar and milk, beating until smooth.
Pipe a swirl of icing onto each cupcake. Roughly chop remaining cookies. Sprinkle cupcakes with cookies and remaining crème de menthe candies.