In a large bowl using a handheld mixer or stand mixer fitted with a paddle attachment, beat the butter for 1 minute on medium speed in a large bowl until completely smooth and creamy. Add the brown sugar and granulated sugar and mix on medium high speed until fluffy and light in color. Beat in egg and vanilla on high speed. Scrape down the sides and bottom of the bowl with a silicone spatula as needed.

In a separate bowl, whisk the flour, cornstarch, baking soda and salt together until combined. On low speed, slowly mix into the wet ingredients until combined. The cookie dough will be quite thick. Add the white chocolate chips, dried cranberries, and pistachios, mix on low for about 5-10 seconds until evenly disbursed. Cover dough tightly with aluminum foil or plastic wrap and chill in the refrigerator for at least 2 hours and up to 2 days. Chilling is mandatory for this cookie dough.

Remove cookie dough from the refrigerator and allow to sit at room temperature for 10 minutes—if the cookie dough chilled longer than 2 hours, let it sit at room temperature for about 30 minutes. This makes the cookie dough easier to scoop and roll. Preheat oven to 350°F (177°C). Line two large baking sheets with parchment paper or silicone baking mats. Set aside.

Once chilled, the dough will be slightly crumbly, but will come together if you work the dough with your hands as you roll into individual balls. Scoop and roll balls of dough, about 1 Tablespoon of dough each, into balls. Bake for 8-10 minutes, until barely golden brown around the edges. They will look extremely soft when you remove them from the oven. Allow to cool for 5 minutes on the cookie sheet. If the cookies are too puffy, try gently pressing down on them with the back of a spoon. They will slightly deflate as you let them cool. Transfer to cooling rack to cool completely.