Line a baking sheet with foil.
Zap the bittersweet chocolate in a medium microwaveable bowl on high until almost melted, 1 to 2 minutes, stirring halfway through the heating time. Stir until completely melted; then mix in the espresso beans. Spread the chocolate mixture on the foil until it’s about ⅛ inch thick. Chill until firm, about 30 minutes.
Meanwhile, crush the candy canes in a zip-top bag with a heavy pan or rolling pin until they’re reduced to small bits (about ½ cup total); set them aside.
Melt the white chocolate as directed for the bittersweet chocolate. Stir in all but ¼ cup of the crushed candy canes. Spread the white chocolate mixture evenly over the hardened dark chocolate mixture. Scatter the reserved candy bits (or sprinkle the sanding sugar) evenly over the top. Chill until firm, about 30 minutes.
Break or cut the bark into irregular pieces and keep them refrigerated in an airtight container for up to 1 month.
Tip: To use this candy for gifting, package the pieces in small decorative boxes or tins tied with ribbon and keep them in the refrigerator.