In a large bowl stir together flour and sugar. Using a pastry blender, cut in butter until mixture resembles fine crumbs and starts to cling. Using a fork, stir in creme de menthe. With clean hands, knead until dough forms a ball (mixture may seem crumbly at first, but as you knead the warmth of your hands will bring dough together). Divide dough in half.
Shape each half into a 6-inch-long log, turning and flattening each side as you turn. Wrap and freeze for 45 minutes to 1 hour or until firm (if dough gets too firm, let stand at room temperature for 10 minutes before slicing).
Preheat oven to 325 degrees F. Cut logs into scant 1/4-inch slices. Place slices 2 inches apart on ungreased cookie sheets. Bake for 10 to 12 minutes or until edges are lightly browned. Transfer to wire racks; cool.
In a small saucepan combine white chocolate and shortening; heat and stir over low heat until melted and smooth. Remove from heat; stir in mint extract. Drizzle over cookies.