Preheat oven to 350°F. In medium bowl, combine flour, baking powder and salt; set aside. In bowl of stand mixer, cream together butter and sugar until light in color and well incorporated. Beat in vanilla and mint extract and egg until combined, scraping down sides as needed. Slowly add flour mixture. If dough gets too thick for mixer finish kneading by hand.
In small batches, roll out dough on floured surface to about 1/4-inch thickness and cut into circles using a biscuit cutter about 2-inches in diameter. Place dough circles on baking sheet covered with parchment paper. Bake 6 to 8 minutes. Remove and let cookies cool on sheets about 5 minutes; transfer to cooling rack to cool completely.
To make ganache, heat cream in small saucepan over medium heat until just starting to bubble, but not boiling. Meanwhile, place chocolate chips and butter in medium bowl. Pour hot cream over chocolate and butter. Let sit 5 minutes undisturbed and then stir until all chocolate is melted and combined. Let cool until mixture is thickened enough to be spreadable.
Once ganache is spreadable, spread it onto one side of half the sugar cookies, spreading ganache all the way to the edge of the cookie. Place an unfrosted cookie on top of ganache, pressing down lightly. Roll edges of each sandwich cookie in crushed candy cane to decorate.