In the bowl of your mixer, cream butter and sugar until light in color and well incorporated.
Beat in vanilla and peppermint extract and egg until combined, scraping down sides as needed.
Meanwhile, combine flour, baking powder and salt. Once egg and extracts are mixed in, slowly add in flour mixture. If your mixer gets mad because the dough is too thick, you can finish it by hand (knead the dough together). If desired, chill dough before rolling.
In small batches, roll out dough on a floured surface to about 1/4-inch thickness and cut into circles – I used a biscuit cutter. Place on cookie sheet.
Bake for 6-8 minutes. Let cool on the cookie sheet until firm enough to transfer to a cooling rack. Cool completely.
To make ganache, heat cream in a small saucepan over medium heat until just starting to bubble, but not boiling. Meanwhile, place chocolate chips and butter in a bowl. Pour hot cream over the chocolate and butter. Let sit for 5 minutes undisturbed and then stir until all the chocolate is melted. Let cool until the mixture is thickened enough to be spreadable.
Once ganache is spreadable, spread it onto one of the sugar cookies, all the way to the edge. Place another cookie on top, pressing down lightly. Immediately roll the edges in candy cane to decorate. Continue this process until all the cookies have been filled and made into sandwiches.