Preheat oven to 350?F. Line 2 baking sheets with parchment paper or a silicone mat.

In the bowl of a stand mixer fitted with a paddle attachment, cream the butter, brown sugar, and granulated sugar until fluffy and light in color, about 1-2 minutes. Scrape the bowl well, then with the mixer on low speed, add the egg and vanilla. Mix until well combined.

Scrape the bowl again and add the flour, cornstarch, baking soda, baking powder, salt, and cinnamon. Mix just until the ingredients are combined. Stir in the chopped pistachios and white chocolate, reserving 1-2 tablespoons of each for the tops of the cookies.

Scoop the dough using a 1-ounce cookie scoop (about 2 tablespoons). Roll each scoop into a ball and press some of the reserved pistachios and white chocolate into the top of each dough ball. Place the cookies onto the prepared pans, spacing them at least 2 inches apart.

Bake at 350?F for 10-12 minutes or until golden brown around the edges. Allow to cool for at least 10 minutes and enjoy!