Combine flour, baking soda and salt in medium bowl; set aside.
Mix Becel® Original margarine with sugars in large bowl. Mix in eggs and vanilla extract until blended. Gradually add in flour mixture; mix just until blended. Stir in additional 1/2 cup (125 mL) flour and peppermint extract. Divide dough in half. Stir cocoa powder into half and candies into the other half. Roll out "white" dough between 2 sheets of parchment or wax paper into 10 x 16-in. (25.4 x 40.6 cm) rectangle. Repeat with "black" dough. Using the parchment paper, place "white" dough on top of "black" dough, trimming excess so dough is even. Gently roll dough lengthwise, using the parchment paper to assist, into log. (Dough will be soft.) Wrap log in parchment paper. Place on cookie sheet and freeze 24 hours.
Preheat oven to 375°F (190° C). Unwrap log and slice into 1/4-in. (6 mm) rounds, rotating the log 1/4 turn after each slice to maintain shape. (Put dough back into freezer between batches.) Place on ungreased cookie sheet. (Cookies might need to be reshaped into circles at this point.)
Bake 7 minutes or until edges are golden. Cool cookies on sheets 2 minutes on wire rack; remove cookies from sheets and cool completely.