Preheat your oven to 350°F (177°C) and line your baking sheet with parchment paper.

In a medium bowl, whisk together all-purpose flour, baking soda, cornstarch, and salt until well combined.

In a large mixing bowl, beat together softened unsalted butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.

Add cocoa powder and vanilla extract to the butter mixture, then beat until fully blended. Add eggs one at a time, mixing well after each.

Gradually add dry mixture to the wet ingredients, mixing gently just until combined. Fold in chocolate chips.

Using a cookie scoop, place dough portions onto the prepared baking sheet, leaving space between each.

Bake for 8–10 minutes until edges are set, centers remain soft.

Allow cookies to cool on the baking sheet for about 5 minutes before transferring to a wire rack.

While the cookies cool, make the peppermint frosting by beating softened butter, then gradually adding powdered sugar, heavy cream, and both extracts.

Once cookies are cooled, frost each with peppermint frosting and sprinkle with crushed peppermint.