1️⃣ Make the Dough:

Cream together butter, brown sugar, and granulated sugar until light and fluffy.

Add egg, yolk, vanilla, and peppermint extract. Mix until combined.

2️⃣ Combine Dry Ingredients:

In another bowl, whisk flour, baking soda, cornstarch, and salt.

Gradually add to wet ingredients, mixing until a soft dough forms.

3️⃣ Add Mix-ins:

Fold in chocolate chips and crushed peppermint pieces until evenly distributed.

4️⃣ Chill the Dough:

Refrigerate for 30–45 minutes to help the dough firm up and prevent spreading.

5️⃣ Bake:

Preheat oven to 350°F (175°C).

Scoop dough into 2-tablespoon balls and place on a parchment-lined baking sheet.

Bake 8–10 minutes, until edges are set and centers are still soft.

6️⃣ Cool:

Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack.