Preheat oven to 350°F. Line two baking sheets with parchment paper or silicone mats.

In a medium bowl, whisk together flour, cornstarch, baking soda and salt. Set aside.

In a stand mixer, beat butter and sugars until light and fluffy. Add egg and vanilla extract.

Add flour mixture, mixing until completely combined. Stir in white chocolate chips and pistachios until evenly distributed. (You can do this by hand or with the stand mixer.)

Roll two heaping tablespoons of dough into a ball. Tear the ball in half and place the torn side down on the cookie sheet. Take the second half and place it on top of the first half - leaving about two inches for spreading.

Bake for 12 minutes, or until the edges are very slightly browned. The cookies will not look cooked in the center, but they will finish cooking while cooling on cookie sheet.

Remove from oven and let cookies rest on baking sheet for 10 minutes. Then transfer to a wire rack to cool completely. Store in an airtight container for up to 7 days.