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

In the bowl of a stand mixer, combine unsalted butter, brown sugar, and granulated sugar; beat until light and fluffy.

Add the room-temperature egg and vanilla extract, mixing on low speed until fully combined.

Gradually add dry ingredients: all-purpose flour, cornstarch, baking soda, baking powder, salt, and cinnamon; mix until just combined.

Gently fold in chopped pistachios and white chocolate, reserving some for topping.

Scoop about 1 ounce of dough onto the baking sheets, spacing at least 2 inches apart; press reserved pistachios and chocolate on top.

Bake for 10-12 minutes until edges are golden; let cool for 10 minutes on the baking sheets before transferring to a wire rack.