Prepare the Cookie Dough: In a large bowl, beat the softened butter and confectioners’ sugar until light and fluffy. Mix in the peppermint extract. Gradually add the flour, cornstarch, and salt, mixing until a soft dough forms.

Chill the Dough: Cover the dough and refrigerate for 30 minutes to make it easier to handle.

Shape and Bake: Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Roll the chilled dough into 1-inch balls and place them 2 inches apart on the prepared baking sheets. Bake for 9-11 minutes, or until the edges are set but not browned. Let cool completely on a wire rack.

Make the Frosting: In a small bowl, beat the butter until creamy. Gradually mix in the confectioners’ sugar, milk, peppermint extract, and food coloring (if using) until smooth and spreadable.

Frost and Garnish: Spread or pipe the frosting over the cooled cookies. Sprinkle crushed peppermint candies on top for a festive finish.

Serve and Enjoy: Let the frosting set slightly before serving. Store in an airtight container for up to 5 days.