In a medium bowl, whisk together the dry ingredients: flour, ground pistachios, cornstarch, baking soda, and salt.

In a large bowl, beat butter, granulated sugar, and light brown sugar until creamy and fluffy for about 2-3 minutes.

Add the egg and vanilla extract to the butter-sugar mixture, mixing until smooth and glossy.

Gradually add dry ingredients into the wet mixture, mixing until just combined to maintain a soft dough.

Gently fold in chopped pistachios and chocolate chunks using a rubber spatula to prevent overworking the dough.

Cover the dough with plastic wrap and chill in the refrigerator for 1-2 hours.

Preheat the oven to 350°F (175°C) and line baking sheets with parchment paper.

Scoop about 2 tablespoons of dough onto the prepared sheets, spacing 4 inches apart.

Bake for 10-11 minutes, until edges are lightly browned and centers are puffy.

Cool on baking sheets for 5-10 minutes before transferring to a wire rack to cool completely.