1. Make the Dough:

• In a large bowl, beat softened butter until creamy (about 1 minute).
• Add confectioners’ sugar and beat until light and fluffy.
• Mix in the egg yolk, vanilla extract, and peppermint extract until combined.
• In a separate bowl, whisk together flour, cornstarch, baking powder, and salt. Gradually add dry ingredients to the wet mixture, beating on low speed until a soft dough forms.
• Cover and chill the dough for at least 30 minutes or up to 3 days.

2. Bake the Cookies:

• Preheat the oven to 350°F (177°C). Line baking sheets with parchment paper.
• Roll dough into 1-tablespoon-sized balls and place them 3 inches apart on the prepared baking sheets. Flatten slightly with your palm.
• Bake for 13–14 minutes until the edges are set but not browned.
• Cool on the baking sheet for 10 minutes, then transfer to a wire rack to cool completely.

3. Make the Frosting:

• In a bowl, beat softened butter until creamy.
• Gradually mix in confectioners’ sugar, milk, vanilla, and peppermint extract until smooth and spreadable.
• If desired, add 1 drop of food coloring and mix until evenly tinted.

4. Decorate the Cookies:

• Spread a generous layer of frosting on each cooled cookie.
• Sprinkle with crushed candy canes and allow the frosting to set at room temperature for 1–2 hours.