MIX flour, cocoa powder, baking powder and salt in large bowl.
BEAT 2 cups sugar, cooled melted chocolate, eggs, oil and peppermint extract in mixer bowl on medium speed until blended. Gradually ADD flour mixture, beating on low speed until blended.
REFRIGERATE, covered, until firm enough to shape, about 1 hour or overnight.
HEAT oven to 350°F. MIX powdered sugar and crushed candy in small bowl. Work with 1/3 of the dough at a time, keeping remaining dough refrigerated. SHAPE dough into 1-inch balls; roll in granulated sugar first and then in crushed candy mixture. PLACE 2 inches apart on parchment paper-lined or ungreased baking sheets.
BAKE in 350°F oven until lightly browned, 8 to 10 minutes. COOL on baking sheets 1 to 2 minutes. REMOVE to wire racks; cool completely.
How to keep your cookies white: Roll the cookie dough ball in granulated sugar before rolling it in the powdered sugar and crushed candy cane mix.
Chilled dough is easier to handle and holds its shape better.