To the bowl of a stand mixer fitted with the paddle attachment, combine the butter, Nutella, light brown sugar, granulated sugar, egg, and vanilla extract, and beat on medium-high speed until creamed and well combined, about 4 minutes. Stop, scrape down the sides of the bowl, and add the all-purpose flour, cornstarch, baking soda, and optional salt, and beat on low speed until just combined, about 1 minute. Stop, scrape down the sides of the bowl, and add the white chocolate chips and semi-sweet chocolate chips, and beat on low speed until just combined, about 30 seconds.