Place unwrapped candy canes or peppermint candies in food processor and pulse until in small pieces. If desired, pour crushed candies through sieve to remove the candy powder from the larger pieces for garnishing the top of the bark. Set aside. Alternately: Place unwrapped candies in a sealing freezer bag. Using a mallet, meat pounder or rolling pin, crush the candies.
Use a small nonstick jelly roll pan or line the jelly roll pan with foil, letting it hang over the sides for easy removal of the finished candy. Grease foil lightly with nonstick spray.
Using a double boiler, heat the semi-sweet chocolate chips over medium-low heat. Heat the chocolate until smooth and lump free. Pour into prepared jelly roll pan. Using a spatula spread the melted chocolate evenly in the pan. To smooth the surface of the shake the pan quickly. Place flat into a refrigerator until cold and firm.
Using a double boiler, heat the white chocolate chips over medium-low heat. Heat the chocolate until smooth and lump free. Remove from heat and stir in peppermint extract. If desired, add 1/2-cup of the candy powder and stir to combine. Pour into jelly roll pan over set semi-sweet chocolate. Using a spatula spread the melted chocolate evenly across the surface of the first. To smooth the candy surface shake the pan quickly. Sprinkle crushed candy across the surface of the white chocolate.
Chill flat until both layers are firm. Trim edges. Cut into 2" squares. Makes approximately 2 pounds.