COOKIES: Position rack in centre of oven, then preheat to 300F. Cut 2 pieces of parchment paper to fit a large baking sheet.
STIR flour with cocoa powder, baking soda and salt in a medium bowl.
USING an electric mixer on medium, beat butter with sugar in a large bowl until fluffy, 1 to 2 min. Beat in milk and peppermint until smooth.
REDUCE speed to low and beat in flour mixture until combined. Form dough into a log and place between parchment paper. (If dough is wet, refrigerate for at least 15 min before forming into a log.) Roll into a 1/8-in. thick 8×12-in. rectangle, then transfer to a baking sheet. Peel off top parchment.
BAKE until firm around edges, about 25 min. Cool for 30 sec in pan. Using parchment paper, place on a work surface. Immediately cut into 1×2-in. rectangles (or any shape desired). Cookies will firm up very quickly. Transfer cookies to a wire rack to cool completely.
DRIZZLE chocolate over cookies until covered. Let stand for 5 min. Using a spatula or palette knife, transfer cookies to a parchment paper–lined baking sheet.
TEMPER white chocolate, then stir in food colouring. Scrape into a piping bag fitted with a small round tip or resealable zip-top bag (cut a very small tip off corner of bag). Pipe decorative lines or designs on top of cookies.
Chatelaine Cookies: How to decorate cookies with royal icing
Nutrition (per serving)
Kitchen Tip: Store in a covered container up to 1 week, or freeze up to 1 month.