Preheat the oven to 350°F/180°C.
Line a nonstick jelly roll pan with parchment paper or a silicone baking mat.
Place the candy canes in a zippered plastic sandwich bag. Lay the bag on a cutting board. Use the flat side of a meat tenderizer to pound the candy until crushed into small pieces.
With an electric mixer set on medium speed, cream the butter until light and fluffy. With the mixer set on low speed, add the yolks and cream. Add the flour, cocoa and salt and mix until the dough comes together. Fold in the crushed peppermint candy.
Roll the dough out to 1/4-in. thickness. Use your favorite shape cookie cutter to cut into individual cookies.
Transfer the cookies to the prepared pan. Chill in the refrigerator for 10 minutes, then bake for 8 - 10 minutes or until the cookies are set.